Novel intelligent lubricating materials and surfaces exhibit on-demand responsiveness and adaptability. The biomimetic self-regulating mechanism empowers in-service tribo-pairs with the autonomy to sense external environmental stimuli and adaptively modulate interfacial lubrication states. Such capabilities provide a groundbreaking solution for the “online sensing-decision-execution” intelligent transformation of advanced equipment in aerospace and defense sectors. Concurrently, the AI-driven intelligent inverse design of lubricating materials has revolutionized the traditional trial-and-error paradigm, enabling highly efficient and demand-responsive customization of lubrication for mechanical interfaces. This innovation provides a novel pathway for establishing a scientific framework for high-performance and high-reliability lubrication materials and surface systems capable of addressing diverse complex operational conditions. The intelligent evolution of lubricating materials and surfaces is progressively redefining the research paradigms in mechanical interface science, potentially unlocking breakthrough opportunities to advance frontier tribological theories and technologies. This paper discusses current research on self-lubricating, self-repairing, and self-diagnosing intelligent lubricating materials and surfaces, the frontier progress of AI-accelerated inverse design, and their future development trends, taking intelligent lubricating materials and surfaces and their AI paradigms as the pointcut. Currently, self-lubricating tribo-pairs that are environmentally robust and operationally adaptable use solid lubricating materials as the matrix, with liquid or solid-liquid-coupled lubricants as the dispersed phase. Effectively enhancing the interfacial lubrication performance can be achieved by releasing trace liquid lubricants to form fluid or boundary films. Two primary approaches are used for incorporating liquid lubricants into a tribo-pair matrix: porous-based self-storing and lubricating strategies and capsule-based self-storing and lubricating strategies. The development of capsule-based self-storage and lubrication techniques makes it a novel solid superlubrication method after carbon-based superlubrication and two-dimensional material superlubrication. This method enables macroscopic superlubrication at temperatures between 0 and 250 ℃. Although intelligent capsule-based self-storing and lubricating technologies can significantly reduce friction and wear on tribo-pair surfaces, material degradation and surface damage are inevitable during prolonged service. It is important to promptly repair wear and damage to improve the wear resistance and service life of tribo-pair materials. Intelligent surface healing technologies for tribo-pairs can be broadly categorized into extrinsic and intrinsic types. Extrinsic repair typically employs stimulus-responsive materials (for example, microcapsules or microvascular networks) to encapsulate active repair agents that are autonomously released upon external stimulus-induced damage, thereby facilitating physicochemical reactions for localized repair. Intrinsic repair leverages the reversible reorganization of dynamic covalent bonds (for example, Diels-Alder (DA) bonds, acylhydrazone bonds, and disulfide bonds) or non-covalent interactions (for example, hydrogen bonds, metal-ligand coordination, and host-guest interactions) to enable autonomous damage repair. Moreover, excessive wear on tribo-pair surfaces generates clearance, and its enlargement exacerbates vibration during equipment operation and reduces service life. Thus, it is imperative to endow tribo-pairs with self-diagnostic capabilities for real-time monitoring of wear locations and damage severity, enabling intelligent lifecycle management and predictive maintenance of equipment. Three approaches are the primary focus of the current intelligent self-diagnostic technologies: dye-based chromatic detection, electrical signal diagnostics, and optical signal diagnostics. The latest paradigm in the research and development of lubricating materials and surfaces, driven by AI, is the fourth paradigm after empirical, theoretical, and computational science paradigms. The primary technical approach involves employing machine-learning models to establish potential mapping relationships between the properties (such as composition and structure) of lubricant materials and surfaces and their lubrication performance. This enables prediction of the lubrication performance of new materials and surfaces. Furthermore, by integrating optimization algorithms or deep-reinforcement-learning techniques, global optimization within the high-dimensional nonlinear design space of lubricant materials and surfaces can be achieved rapidly, thereby facilitating the efficient inverse design of materials and surfaces with target attributes. This transformative research paradigm is expected to decipher the lubrication and friction reduction mechanisms at mechanical interfaces, overcome the efficiency limitations of traditional trial-and-error iterative methods, and ultimately realize demand-driven customization of lubricant materials and surface designs.

Thermal barrier coatings (TBCs) technology has been widely employed in the thermal protection of aero-engine blades. The blade surfaces are coated with ceramic materials that exhibit excellent thermophysical properties, high-temperature stability, mechanical strength, and resistance to high-temperature corrosion, thereby ensuring the longevity of aero-engines. However, the traditional 6wt.%-8wt.% Y₂O₃-stabilized ZrO₂ (YSZ), commonly used to prepare TBCs, undergoes a phase transition with severe volume expansion, rapid sintering and severe high-temperature melt corrosion above 1 200 ℃, leading to premature coating failure. To address the increasing service temperature of high-performance aero-engine, developing the novel TBCs material is urgently required. Recent advancements in research of ‘high-entropy' alloys have inspired the application of the composition design of novel ceramic materials. The synthesis and performance evaluation of high-entropy ceramic materials have thus provided new avenues for the development of novel TBC materials. The outstanding performance of the high-entropy ceramic materials is primarily attributed to four inherent effects: ① thermodynamically high-entropy effect; ② dynamically sluggish diffusion effect; ③ severe lattice distortion; ④ cocktail effect. Relevant studies have demonstrated that these four distinctive effects associated with high-entropy materials provide a degree of flexibility in composition design and property regulation, which is not present in traditional TBCs or single-component TBCs materials. Furthermore, the comprehensive performance of high-entropy TBCs ceramics is comparatively better, as evidenced reduced thermal conductivity, a coefficient of thermal expansion (CTE) that is well-matched with the alloy substrate, and the exceptional high-temperature stability. This paper presents a summary of the current research status of high-entropy thermal barrier ceramics offering an analysis of component design and performance optimization based on the characteristics and the nature of bonding in the crystal structure. The analysis covers five key aspects: thermal conductivity, thermal expansion performance, high-temperature resistance to sintering and phase stability, mechanical properties and resistance to high-temperature CaO-MgO-Al₂O₃-SiO₂ CMAS corrosion. Elements with large mass disorder and ionic radius disorder are used for the synthesis of high-entropy TBCs materials to form a larger degree of lattice distortion, which can expand the phonon collision chances, decreasing the phonon mean free path and reducing the thermal conductivity. Anions and cations with minor differences in electronegativity can form ionic bonds with weak bonding strengths to obtain materials with higher CTE. Similarly, the formation of ionic bonds with strong bonding strength is beneficial for improving the mechanical properties, such as hardness and fracture toughness. The ions with the large radius difference compete for the same lattice site together, forming a more severe lattice distortion, which hinders matter diffusion. It leads to the sluggish diffusion phenomenon that contributes to high temperature stability. The concept of high entropy, based on the nature of multi-component single-phase solid solutions, offers a novel approach to the composition design and property regulation of novel TBCs materials, which has attracted considerable research interest. By summarizing and analyzing the radius disorder, mass order, and bond strength, the high-entropy thermal barrier ceramics with optimized composition based on the nature of ion can exhibit enhanced thermal physical properties, CTE, mechanical properties, high-temperature resistance to sintering and phase stability, and resistance to CMAS corrosion, exhibiting the potential for further development. However, the preparation and performance of high-entropy thermal barrier ceramic materials is the research mainstream, which is not entirely applicable. Moreover, several problems need further research and to provide solutions during manufacturing, thereby promoting its development and maturity, such as element segregation and phase transition. In this study, the theoretical guidance on the composition, design, performance optimization, and regulation of high-entropy TBCs materials and an outlook on the prospective applications is offered.

Nickel-based single-crystal superalloys are widely used in aviation and industrial gas turbine blades owing to their excellent mechanical properties at high temperatures. However, under extreme service conditions, these superalloys are susceptible to fatigue, wear, corrosion, and oxidation damage, which pose significant risks to engine safety. Laser shock peening (LSP) is an advanced surface-strengthening technology that utilizes laser shock waves to induce severe plastic deformation at the surface, alter the microstructure, and introduce compressive residual stress (CRS), thereby enhancing the fatigue resistance and other properties of the alloy. Some studies have investigated the laser shock strengthening of nickel-based single-crystal superalloys for turbine blades. However, there is a notable lack of a systematic summary on this topic. This study begins by examining the technical characteristics of various LSP technologies, including traditional high-energy laser shock, low-energy laser shock without an absorption layer, warm LSP (WLSP), and femtosecond LSP (Fs-LSP). The effects of these technologies on the microstructures and properties of nickel-based single-crystal superalloys are compared, highlighting their respective advantages and disadvantages. This summary revealed that the strengthening effects of various LSP technologies on single-crystal superalloys differ. Ns-LSP and WLSP can achieve millimeter-level strengthening layer depths; LSPwC reaches several hundred micrometers; and Fs-LSP results in depths of tens of micrometers. The strengthening mechanisms of the four LSP processes for nickel-based single-crystal superalloys are distinct. Ns-LSP primarily strengthens by introducing high-density crystal defects and CRS during the shock process. WLSP improves the density, uniformity, and stability of crystal defects. LSPwC not only introduces crystal defects and CRS but also generates in-situ nano-oxide particles that further impede the dislocation motion, enhancing the strengthening effect. Fs-LSP introduces both crystal defects and CRS, and simultaneously builds surface periodic micro-nanostructures, achieving a synergistic optimization of strengthening effect and functional structure. Each of these processes has unique features and provides diverse technical paths for the performance enhancement of single-crystal alloys. Despite the different depths of strengthening layers, the core mechanism of these techniques lies in the large number of crystal defects and CRS introduced by LSP. The large plastic deformation induced by Ns-LSP and WLSP may lead to recrystallization of the single-crystal superalloy during the strengthening/service process, thereby damaging its high-temperature creep performance. Therefore, further research is needed to explore how LSP technology can achieve efficient and high-quality strengthening of single-crystal superalloys, and obtain ideal single-crystal structures. When LSPwC is used to strengthen single-crystal superalloys, the laser directly acts on the alloy surface, leading to surface remelting and oxidation, which in turn reduces the surface quality. Therefore, further research is required to improve the surface quality of the LSPwC-treated single-crystal superalloys and enhance their strengthening effect. The paper also discusses the challenges and difficulties faced in the LSP of nickel-based single-crystal superalloys and offers insights into future development trends. LSP technology has already been commercially applied in other alloy fields, and research has shown that it can improve issues such as fatigue, wear, oxidation, and corrosion in nickel-based single-crystal superalloys. To further advance this technology and expand its market penetration, it should be developed in several directions: composite strengthening process innovation, upgrading of residual stress detection equipment, innovations in equipment manufacturing technology, and the establishment of intelligent processing systems.

Accelerator-based boron neutron capture therapy (AB-BNCT) has attracted significant attention as an emerging cancer-treatment technology. The establishment of a stable neutron production target system is crucial, and the design and fabrication of a reliable anti-hydrogen embrittlement layer is crucial in ensuring long-term stability. This study investigates the effects of substrate pretreatment on the structure and performance of an anti-hydrogen embrittlement layer for accelerator-based neutron production. The substrates were treated using glass beads of varying mesh sizes, followed by the deposition of tantalum (Ta) coatings of different thicknesses via magnetron sputtering. This approach facilitated the analysis of the growth mechanism of the Ta coatings on pretreated substrates. Laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM) were used to examine the substrate microstructure before and after sandblasting. The surface roughness was evaluated using LSCM before and after film deposition. The results revealed that as the glass bead mesh size increased from 36 to 360, the surface roughness of the substrate decreased from 5.76 nm to 1.53 nm, representing a reduction of 4.23 nm. A moderate increase in the roughness of the surface enhanced the adhesion of the anti-hydrogen embrittlement layer to the substrate, thereby improving its protective performance. SEM and LSCM observations indicated that the deposited coating inherited the initial morphology of the substrate, forming a continuous layer at a thickness of 5 μm. The crystal structure of the anti-hydrogen embrittlement layer was analyzed by X-ray diffraction (XRD), and the chemical properties of the films were further investigated by X-ray photoelectron spectroscopy (XPS). Finally, stress measurements were conducted to evaluate the overall quality of the films. However, at a thickness of 20 μm, samples with higher surface roughness exhibited growth-induced voids. X-ray diffraction (XRD) analysis revealed that, as the coating thickness increased, the crystallographic structure of the Ta coating evolved on the copper (Cu) substrate. During the nucleation stage (1 μm), α-Ta was preferentially formed, whereas during the growth stage, α-Ta gradually transformed into β-Ta. When the coating thickness reached 20 μm, samples with lower roughness were predominantly composed of the β phase. Increased roughness contributed to grain refinement; however, for coatings beyond a certain thickness, finer grains were observed in samples S4 (5 μm) and S5 (20 μm). No cracks or delamination were observed in the 20 μm-thick Ta coatings deposited on all pre-treated substrates. Film quality was further assessed through stress measurements, revealing an inverse relationship between coating thickness and internal stress. Measurements demonstrated a significant stress reduction with increasing film thickness. This reduction was attributed to the stronger influence of the substrate on 1 μm-thick coatings. Notably, after sandblasting the substrate with 360-mesh glass beads, the stress of the 20 μm-thick Ta coating was reduced to only 0.35 GPa. Additionally, the pits generated by sandblasting induced compressive stress during the intermediate growth stage, promoting adhesion between the Ta antihydrogen embrittlement layer and substrate. Comparative analysis of different samples demonstrated that, under identical magnetron sputtering parameters, substrates treated with 220-mesh glass beads exhibited a smooth and dense surface morphology, with the corresponding 20 μm-thick Ta coating exhibiting a stress level of only 0.35 GPa. The fabrication of an anti-hydrogen embrittlement layer was successfully achieved by sandblasting pre-treatment combined with magnetron sputtering. An optimal sandblasting mesh size was selected to ensure reliable adhesion of the subsequent lithium reaction layer. This study provides valuable insights into the development of stable and efficient accelerator-based neutron production targets for AB-BNCT while addressing critical engineering challenges when implementing anti-hydrogen embrittlement layers in accelerator-driven neutron production targets.

Cold-sprayed Zn coatings have attracted considerable attention as a topic of active research in materials science and surface engineering owing to their superior resistance to corrosion. Thus, techniques based on cold-sprayed Zn coatings have been developed rapidly over the past few decades, with a focus on enhancing their performance and broadening potential areas of application. In this study, we provide an in-depth review of recent works on cold-sprayed Zn coatings to offer a comprehensive summary of advancements in pure Zn, Zn-alloy, and Zn-based composite coatings. First, we examine the microstructure and properties of cold-sprayed pure Zn coatings. Studies have shown that the deposition process results in a unique microstructure characterized by fine grains and high density, which confers excellent initial resistance to corrosion. However, it still needs some improvement in terms of the mechanical properties of the coatings such as their hardness and tensile strength. Research efforts have concentrated on optimizing spraying parameters such as gas pressure and temperature to enhance the density and uniformity of the coatings to improve their overall performance. Secondly, we systematically review the relevant literatures on cold-sprayed Zn coating, Zn-alloy coating, and Zn-ceramic composite coating. The adding elements such as Al, Mg, or Ni can significantly alter the microstructure and properties of Zn coatings. For example, studies have shown that the formation of intermetallic compounds in Zn-Al alloy coating plays a crucial role in enhancing corrosion resistance and mechanical strength. These compounds act as barriers against corrosion and strengthen the coating. In Zn-ceramic composite coating, the incorporation of ceramic particles such as alumina (Al₂O₃) or titanium dioxide (TiO₂) can improve coating’s hardness and wear resistance. A study on Zn-Al₂O₃ coating found that the wear rate of the coating was significantly reduced under specific tribological test conditions with the addition of a certain proportion of Al₂O₃ particles. The key findings of these studies provide valuable insights to guide future research and development. Additionally, we also review the common additive phases in cold-sprayed Zn coatings and their impacts on mechanical and tribological properties and corrosion resistance. Adding materials such as graphene, carbon nanotubes, and various nanoparticles have been introduced to achieve synergistic effects. For example, graphene forms a barrier layer within Zn coating that remarkably enhances its resistance to corrosion. Research indicates that when an appropriate amount of graphene is added to Zn coating, the corrosion current density is greatly reduced compared with Zn coating, which indicates a significant improvement in corrosion resistance. These additions can also improve tribological properties and reduce friction and wear. Furthermore, we also summarized post-treatment technologies such as heat treatment and shot peening. The influence of these post-treatment methods on cold-sprayed Zn-based coatings are evaluated based on experimental results and theoretical analysis. In general, heat treatment can relieve internal stress, improve crystallinity, and enhance the bonding strength between the Zn-based coating and the substrate. In an experiment with heat treatment, the adhesive strength was increased significantly when the samples were heated to an appropriate temperature and maintained for a certain period. Similarly, shot peening can refine surface grains, increase the surface hardness, and enhance fatigue resistance. Finally, we also outline prospects for future developments in cold-sprayed Zn-based coatings. It is expected that more advanced spraying techniques and new adding materials will emerge to further optimize the performance of cold-sprayed Zn-based coatings.

Marine biofouling poses a persistent challenge for submerged mechanical equipment, leading to accelerated corrosion, operational inefficiencies, and significant economic losses. The accumulation of microbial communities on marine surfaces not only damages equipment but also substantially increases maintenance costs, creating a critical bottleneck for sustainable marine resource development. Addressing this issue through effective antifouling solutions has become a global research priority in marine engineering. Current antifouling technologies primarily encompass mechanical removal, ultrasonic cleaning, and protective coatings, with antifouling coatings emerging as the most widely adopted solution due to their cost-effectiveness, ease of application, and superior performance. There is a wide variety of antifouling coatings, each with distinct antifouling mechanisms. However, comprehensive reviews on the antifouling performance, advantages, and disadvantages of both traditional and novel antifouling coatings remain scarce. Thus, a comprehensive review is conducted on the research advancements of both traditional and novel antifouling coatings, such as natural antifoulant coatings, biomimetic coatings, self-healing coatings, etc. Their research status, antifouling mechanisms, and remaining challenges are discussed. Traditional antifouling coatings can be categorized into matrix-insoluble and matrix-soluble types. The former operate through the gradual release of embedded biocidal compounds that deter or eliminate fouling organisms. However, these coatings exhibit significant limitations, including short service lifetimes and complex application requirements, which restrict their widespread adoption in marine applications. Self-polishing antifouling coatings (SPCs), the most currently commercially successful matrix-soluble system, dominating 90% of the global market, utilize hydrolyzable polymer side chains to enable controlled antifoulant release. However, their uneven release kinetics (initial excess followed by insufficiency) compromises long-term performance, and their dependence on toxic biocides raises environmental concerns. In contrast to these traditional coatings that rely on biocidal agents, fouling-release coatings achieve antifouling effects solely through their low surface energy, preventing fouling organisms from firmly adhering. Under water flow, fouling organisms detach easily, providing excellent antifouling performance without harming the marine environment. However, these coatings perform poorly under static conditions, and their adhesion to substrate needs improvement. Natural antifoulant coatings derive their active substances from antifouling compounds secreted by plants and animals or their synthetic analogs. They reduce marine biofouling by inhibiting adhesion processes and interfering with microbial signaling systems. Compared to traditional antifoulants, natural antifoulants are less toxic and significantly reduce environmental impact. However, challenges such as broad-spectrum efficacy and long-term durability remain unresolved. Biomimetic coatings utilize micro- and nanostructures from self-cleaning natural surfaces (via 3D printing, laser etching, or transfer techniques) to achieve efficient and eco-friendly antifouling effects, showing high application potential. However, these coatings often suffer from low mechanical strength, poor adaptability, and high production costs. Self-healing marine coatings integrate specialized repair agents that autonomously mend surface damage, overcoming key limitations of conventional systems by extending service life and maintaining antifouling efficacy. Despite their potential for significant economic and performance benefits, commercialization challenges persist, including complex fabrication, high costs, and difficulties in scaling beyond laboratory prototypes. Photocatalytic coatings rely on photocatalysts to undergo redox reactions under specific light wavelengths, decomposing seawater and dissolved oxygen to generate reactive oxygen species (ROS). These ROS penetrate cell membranes, damage microbial DNA, and cause cell rupture, achieving antifouling through microbial inactivation. These coatings are safe, efficient, non-toxic, and pollution-free. However, their performance is highly dependent on UV intensity and light energy utilization, requiring further improvements in stability. Hydrogel coatings contain high water content (typically >70%, even >90%), forming a dense and dynamic hydration layer through hydrogen bonding between polymer chains and water molecules. This layer effectively blocks fouling organism attachment. However, their poor mechanical properties and weak adhesion limit broader applications. Despite the variety of marine antifouling coatings available, single mechanism approaches generally fail to meet the complex demands of marine environments, particularly regarding long-term efficacy, broad-spectrum performance, and environmental safety. To overcome these limitations, we propose the strategic integration of multiple antifouling mechanisms within hybrid coating systems. This synergistic approach aims to combine the advantages of different technologies while mitigating their individual weaknesses, paving the way for next-generation antifouling solutions that balance performance, durability, and ecological sustainability. The findings provide valuable insights for developing advanced marine coatings.

The accelerated development of modern industry and information technology has resulted in a notable surge in demand for high-performance materials capable of functioning in extreme environments, particularly in the domains of friction and electromagnetic wave absorption. MXene-based materials have attracted considerable interest owing to their exceptional properties, including high electrical conductivity, a unique layered structure, outstanding mechanical properties, chemical stability, and abundant surface functional groups. However, a comprehensive and systematic review of recent progress in the application of MXene-based materials in tribology and electromagnetic wave absorption remains unavailable. To address this gap, an in-depth and systematic review of the structural properties, preparation methods, and performance mechanisms of MXene-based materials in these applications is presented. The fundamental structural characteristics of MXene are examined, including its two-dimensional configuration, chemical composition, and surface modifications. These attributes are considered to be critical in understanding the multifunctional performance of MXene. Furthermore, the intrinsic properties of MXene, including its exceptional electrical conductivity and mechanical flexibility, are analyzed in detail. The preparation and processing techniques of MXene and its derivatives are also explored, with a focus on the ways in which various processes, ranging from conventional wet chemical etching to advanced composite fabrication methods, are employed to tailor MXene materials for specific performance requirements. In the field of tribology, MXene-based materials have the potential to significantly reduce friction and enhance wear resistance. The preparation and processing of MXene has been the subject of considerable study, and the results have highlighted notable advantages over traditional two-dimensional materials, such as graphene and molybdenum disulfide. In particular, the achievement of lower coefficients of friction and wear rates has been demonstrated. These superior tribological properties are primarily attributed to the unique two-dimensional structure and surface chemistry of MXene. The integration of MXene into lubricants or composites has been demonstrated to enhance friction reduction and anti-wear performance, yielding coefficients of friction and wear rates that exceed those of conventional materials. Furthermore, MXene functions effectively as a cross-linking agent in polymer systems, significantly improving their tribological characteristics by reinforcing their mechanical integrity and enhancing surface interactions. In the field of electromagnetic wave absorption, MXene-based materials demonstrate exceptional wave energy attenuation capabilities, attributable to their high electrical conductivity, superior dielectric loss, and tunable surface chemistry. These properties facilitate the efficient conversion of electromagnetic energy into other forms of energy, enabling optimal absorption performance across a wide frequency range. The surface functionalization and formation of composites with materials such as polymers, magnetic nanoparticles, or carbon-based structures have further enhanced the efficiency and bandwidth of the absorption process. Furthermore, the layered structure of MXene facilitates multiple internal reflections of electromagnetic waves, thereby significantly enhancing its absorption capabilities. A comparative analysis of various composite designs and processing techniques demonstrates that MXene-based materials outperform traditional wave-absorbing materials, such as ferrite and carbonyl iron powders, particularly in lightweight and flexible applications. These advantages position MXene-based materials as a highly promising solution for modern electronic devices, stealth technology, and electromagnetic interference shielding, addressing critical demands in these advanced technological fields. Despite the remarkable properties and potential of MXene-based materials across a range of applications, a number of challenges remain. These include stability issues under extreme conditions, such as limited resistance to oxidation and thermal degradation, as well as the complexity involved in designing multifunctional composites and the high costs associated with large-scale production. To overcome these obstacles, several improvement strategies are proposed. These include surface functionalization to enhance environmental stability, the integration of MXene with other nanomaterials to augment multifunctionality, and the optimization of preparation processes to reduce production costs. The implementation of these strategies is expected to significantly broaden the practical applications of MXene-based materials, thereby rendering them more feasible for industrial and technological use. In conclusion, the present study offers a systematic review of the research progress on MXene-based materials in the fields of tribology and electromagnetic wave absorption. This includes a detailed analysis of their unique properties, underlying mechanisms, and preparation methods. The findings provide a comprehensive understanding of the current advancements while identifying critical challenges and future research directions. Given their exceptional performance characteristics and versatile potential, MXene-based materials are anticipated to play a pivotal role in addressing the demands of modern industry and advanced technologies. It is likely that their continued development will yield innovative solutions for applications in high-performance friction materials, electromagnetic interference shielding, and beyond, underscoring their importance as a transformative material platform.

Owing to their remarkable combination of high strength and superior corrosion resistance, titanium alloys have found extensive applications across a diverse range of industries, including aerospace and biomedicine. However, the difficult-to-machine nature of titanium alloys leads to poor surface quality and low material removal rates during conventional grinding. To overcome the limitations of conventional titanium alloy grinding processes, energy field-assisted machining has become a research hotspot. Ultrasonic-assisted grinding (UAG) couples high-frequency, low-amplitude vibrations with conventional grinding motions to create a periodic “contact-separation-contact” machining pattern between the workpiece and tool. This alters the material removal mechanism, significantly reduces grinding forces and temperatures, and improves the surface integrity of the workpiece. This paper first analyzes the coupled motion characteristics of ultrasonic vibrations, covering one-dimensional vibration modes such as axial, radial, and tangential modes, as well as two-dimensional and three-dimensional composite vibrations. These vibration modes can alter the trajectory of abrasive grains, shorten the effective contact arc, enhance chip removal, and promote material removal dominated by intermittent shearing. This paper summarizes numerical simulation and analytical modeling methods to explain the evolution of undeformed chip thickness, local plastic deformation, and thermo-mechanical interactions under ultrasonic assistance. Furthermore, it reviews various grinding force models developed for different vibration modes to elucidate how ultrasonic vibration affects deformation forces, plowing resistance, and frictional behavior. Experimental observations consistently demonstrate that ultrasonic-assisted grinding improves surface integrity and reduces tool wear. Previous research has shown that ultrasonic-assisted grinding can improve surface quality by 30%-50% and reduce tool wear by up to 40%. In addition, this paper discusses tool wear mechanisms such as abrasive microcracks, bond degradation, and adhesive wear, focusing on the role of ultrasonic vibration in maintaining cutting edge sharpness and enhancing self-sharpening. Surface morphology prediction and subsurface damage modeling further demonstrate that ultrasonic vibration can improve surface finish, suppress surface defects, and contribute to a more favorable residual stress state in titanium alloy parts. Besides single-field ultrasonic grinding, this paper also explores the rapid development of multi-energy-field ultrasonic grinding technology. Representative methods include ultrasonic-plasma oxidation, ultrasonic-electrochemical grinding, ultrasonic-micro-lubrication, ultrasonic-jet-assisted grinding, and ultrasonic-mechanical-chemical coupling. These hybrid methods utilize the synergistic effect of ultrasonic vibration and additional physical or chemical energy fields to enhance lubrication, reduce friction, promote material removal, and stabilize temperature rise during grinding. This hybrid approach also helps improve surface integrity and more effectively control the grinding interface. Combining multiple energy fields with ultrasonic vibration opens up new possibilities for further improving machining performance, especially for difficult-to-machine materials such as titanium alloys. This paper reviews the current research progress, theoretical framework, and mechanistic insights into ultrasonic-assisted grinding and multi-energy field grinding of titanium alloys. The research results provide valuable guidance for advancing efficient, high-precision, and low-damage grinding technologies.

C_f / SiC composites are characterized by high hardness, high brittleness, anisotropy, and heterogeneity, which induce machining defects such as matrix cracking and fiber pull-out during conventional mechanical processing, severely undermining the service performance and lifespan of components. To address this challenge, a novel single-excitation longitudinal-torsional ultrasonic elliptical vibration turning (LTUVT) device was designed and developed in this study. The primary objective was to achieve stable elliptical tool-tip motion through a simplified vibration system, thereby improving the machinability of the C_f / SiC composites. This study was conducted systematically, encompassing structural design, theoretical analysis, simulation verification, performance testing, and machining experiments. First, based on the principle of longitudinal-torsional vibration coupling, the core components of the device—the transducer and the horn—were structurally designed. Spiral grooves with the defined parameters were machined onto the horn surface. This design decomposes the longitudinal vibration generated by a single piezoelectric ceramic excitation into longitudinal and torsional vibration components with a specific phase difference. The three-dimensional elliptical trajectory of the tool tip, superimposed with the workpiece rotation, tool feed, and ultrasonic vibration, was analyzed through kinematic modeling. Motion equations were derived to elucidate the conditions for intermittent cutting and the friction reduction mechanism. Second, the dynamic characteristics of the designed transducer were investigated via finite element analysis using the COMSOL software. Modal analysis identifies an ideal longitudinal-torsional coupled vibration mode near 21 830 Hz, with the maximum amplitude concentrated at the output end and nearly zero amplitude at the flange, validating the structural rationality. Harmonic response analysis further shows that the longitudinal and torsional amplitudes at the output end at the target frequency are approximately 15 and 10.5 μm, respectively, with a ratio of about 0.7, falling within the preset range of 2-15 μm. Subsequently, the vibrational performance of the fabricated turning device was experimentally tested. The impedance analysis shows that the actual resonant frequency is 21 061 Hz, with a deviation of 5.3% from the preset frequency of 20 000 Hz. The admittance circle is well-formed, indicating good resonant characteristics. Amplitude testing using a laser Doppler vibrometer demonstrates that both longitudinal and torsional amplitudes increase synchronously with the ultrasonic power supply’s output power, reaching maximum values of 12.84 and 11.2 μm, respectively, with an average ratio of about 0.9. These results are consistent with the simulation and design expectations, confirming the capability of the device to deliver stable and controllable elliptical vibrations. Finally, systematic comparative turning experiments were performed on the prepared C_f / SiC composite workpieces using polycrystalline diamond (PCD) tools. The influence of ultrasonic amplitude on the cutting forces, workpiece surface morphology, and tool wear was comprehensively investigated. The results indicate that the LTUVT significantly reduces the cutting forces. Compared with the CT, under the optimal parameters, the radial force, main cutting force, and feed force are reduced by an average of 25.8%, 23.9%, and 26.4%, respectively. Cutting forces decrease continuously with increasing ultrasonic amplitude, reaching minimum values (F_x=3.3 N, F_y=8.8 N, F_z=4.9 N) at a longitudinal amplitude of 9 μm. The LTUVT effectively suppresses the machining damage. Compared to the significant fiber pull-out, matrix cracking, and chip adhesion observed in CT, LTUVT promotes material removal modes dominated by fiber shear and brittle fractures. The fewest defects, such as fiber pull-out and pits, and maximum surface integrity are achieved at a longitudinal amplitude of 6 μm. LTUVT substantially mitigates tool wear. In contrast to the deep and continuous wear-land formed on the tool flank face in CT, LTUVT results in shallower wear grooves and a smaller wear-land area. The tool flank wear area first decreases and then increases with increasing amplitude, reaching a minimum average value of 50 150 μm² at a longitudinal amplitude of 6 μm, representing a reduction of approximately 79.95% compared to CT. However, excessive amplitude (9 μm) leads to aggravated micro-chipping of the cutting edge. The optimal process parameter identified is a longitudinal amplitude of 6 μm (corresponding to a torsional amplitude of approximately 5.4 μm), which balances superior surface quality with minimal tool wear. This study provides an effective ultrasonic vibration-assisted machining solution for the precise and efficient processing of difficult-to-machine composites, such as C_f / SiC, with significant theoretical and practical engineering value.

Mobile additive repair and remanufacturing in complex on-site environments face three overarching challenges: the multi-constrained nature of operational conditions and repair targets, discrete and highly variable quality domains of service-degraded materials, and demand for precise control and reliable assessment of repair quality in dynamically changing field scenarios. To address these challenges, this review examines the connotations, technical characteristics, and intrinsic difficulties associated with mobile additive repair and remanufacturing, with particular emphasis on the unique requirements of on-site operations. Drawing on recent developments and practical application cases, this article outlines the system composition, core modules, and functional architecture of mobile additive repair systems, including mobile deployment platforms, digital modeling and reconstruction tools, adaptive material-process subsystems, and multidimensional sensing and evaluation frameworks. By analyzing advances in design, materials, processes, and equipment, this review highlights the emergence of integrated mobile systems capable of operating in constrained spaces, interacting with heterogeneous surface states, and maintaining deposition stability under fluctuating environmental conditions. This study further analyses the main research directions and representative technical routes that shape the development of mobile additive repair technologies. These include environment-aware process planning strategies that consider geometric limitations, thermal boundary shifts, and accessibility constraints; material adaptation methodologies designed to accommodate substrate degradation, oxidation, or microstructural heterogeneity; and intelligent thermal and shielding control approaches that stabilize melt-pool behavior and improve layer quality in open or partially confined environments. Substantial progress has also been made in real-time monitoring and multiscale quality evaluation, where optical, infrared, acoustic, and laser-based sensing are increasingly combined to track dilution, defect initiation, interfacial bonding, and microstructure evolution during deposition. Based on these developments, this review identifies several key enabling technologies that enable reliable onsite additive repair of components located in special environments or within large-scale equipment that cannot be disassembled. Representative advances include portable and modular mobile repair platforms with enhanced environmental adaptability, digital twin-assisted repair workflow designs that link defect characterization with predictive simulation, and adaptive process control frameworks responsive to real-time disturbances. These innovations collectively form a new technical system that unifies design methodologies, material strategies, process optimization, equipment engineering, and closed-loop quality assurance. Across multiple industrial case studies, such integrated technical systems have demonstrated strong potential for delivering high-quality and efficient on-site repair of damaged components, ranging from turbine casings and reactor vessels to heavy machinery parts and aerospace structures. Commonly reported improvements include enhanced deposition uniformity in restricted or variable environments, stronger metallurgical bonding to service-degraded substrates, reduced incidence of common defects such as porosity or microcracks, and more predictable dimensional restoration with lower post-processing requirements. By consolidating these advances and mapping their interconnections, this review provides a coherent perspective on the evolution of mobile additive repair and remanufacturing technologies. Simultaneously, it identifies persistent scientific and engineering challenges—such as robust material-process matching for severely degraded substrates, more reliable prediction of repaired-component lifecycle performance, and further miniaturization and intelligent control of mobile platforms—that are likely to drive future research. Overall, this review summarizes the progress in establishing a new generation of mobile additive repair systems capable of providing high-quality, efficient, and reliable on-site restoration of critical components for the energy and chemical industries, heavy-duty equipment, and aerospace applications, and outlines the technological foundations required for continued advancement in this rapidly developing field.

The development of precision medicine requires efficient, stable, and multifunctional biomechanical interfaces. The abundant micro / nanostructures and functional mechanisms found in nature provide important inspiration for interface design; however, research on biomimetic bio-machine interfaces for precision medicine still lacks in-depth and systematic reviews. This paper systematically summarizes representative biomimetic strategies in interface design, with a particular focus on the principles and applications of antifouling, adhesion enhancement, directional liquid transport, and microneedle penetration structures in interface construction. It further discusses the advantages and limitations of advanced manufacturing technologies, such as laser processing and 3D printing, for the fabrication of multiscale biomimetic structures. Typical applications in precision medicine, including antifouling electrosurgical scalpels, adhesive patches, wearable microfluidic diagnostic sensors, and drug delivery systems, have demonstrated the remarkable benefits of biomimetic structures for improving interfacial adaptability, functional integration, and clinical applicability. Finally, this study explores the crucial role of emerging technologies, such as artificial intelligence, stimuli-responsive materials, and multi-material 3D printing, in driving the advancement of biomimetic bio-machine interfaces. Despite notable progress in biomimetic design and manufacturing, this field remains in its early stages and faces multiple challenges. For instance, natural multifunctional interfaces often exhibit highly complex material compositions and hierarchical multiscale features, making high-precision and consistent biomimetic reconstruction across the macro- and microscales highly dependent on breakthroughs in advanced manufacturing. Current biomimetic approaches are largely confined to isolated structural or material mimicry, with limited progress in the integrated codesign of structures, materials, and functions. Moreover, the intelligent responsiveness and multifunctional integration of interface systems remain underdeveloped, and achieving external-field-driven control (e.g., mechanical, thermal, acoustic, optical, electrical, and chemical) of interface properties is key to advancing system intelligence. Currently, most biomimetic functional interfaces remain in the proof-of-concept stage, and their long-term durability, biocompatibility, and safety require further validation for clinical and real-world applications. Biomechanical interfaces are expected to evolve beyond static designs to dynamic and adaptive systems. By integrating stimuli-responsive materials with flexible sensing networks, such interfaces can achieve real-time environmental perception and feedback regulation, enabling closed-loop intelligent medical devices, such as adaptive neural interfaces and dynamic drug-delivery microneedle arrays. Multiscale simulations (e.g., molecular dynamics and finite element analysis) can accurately predict the mechanical, electrical, and biological behaviors at the interface. Furthermore, coupling biomimetic design with artificial intelligence, particularly machine and deep learning, promises to establish data-driven platforms for interface design, enabling an integrated workflow from natural structure extraction and material selection to manufacturing pathway planning and performance prediction, thus advancing the paradigm from experience-driven to data-driven biomimetic design. Breakthroughs in key technologies such as multimaterial cooperative printing and scalable micro / nanoscale manufacturing are critical for establishing standardized and modular fabrication systems with improved reproducibility and consistency. Simultaneously, systematic frameworks for long-term biocompatibility assessment must be developed to ensure clinical safety and stability. In summary, this study proposes two guiding strategies—dynamic biomimetic design enabled by smart materials and intelligent interface design enabled by artificial intelligence—to fill a critical gap in the literature. These perspectives provide valuable insights for the future development of biomimetic interface design and manufacturing for precision medicine.

Thermal barrier coatings (TBCs) are a core technology for protecting hot-end components in the aerospace, aviation, and energy sectors and play a critical role in ensuring the safe and stable operation of these high-temperature systems. Since the concept of TBCs was proposed by NASA in the 1950s, this vital technology has gone through nearly 80 years of continuous development and evolution. During this period, several researchers worldwide devoted tremendous time, energy, and expertise to advancing its material systems, preparation processes, and overall performance, laying a solid foundation for its widespread application in key industries. With the rapid development of high-entropy alloys (HEAs) and high-entropy ceramics (HECs) in recent years, high-entropy materials engineering has emerged as a crucial and promising development direction for TBC material systems. This shift toward high entropy has created new avenues for overcoming the performance limitations of traditional TBC materials. However, systematic reviews that comprehensively discuss the structural evolution of coatings, their damage mechanisms, and innovation directions in the context of high-entropy engineering remain relatively scarce. This limitation makes providing effective theoretical and technical support for collaboration between research and practical applications in the TBC field difficult, hindering the translation of lab-based achievements into industrial practice. To address this gap, this paper systematically sorts out the changes in TBC demand driven by the continuous advancements in industrial production (such as energy equipment upgrades) and aerospace transportation (including aircraft and spacecraft development) from the perspective of the need for heat management and control. It shows that the operating conditions of hot-end components (such as gas turbine blades and aero-engine parts) are gradually breaking through the 1200 ℃ temperature resistance limit of traditional TBCs, making it urgent to research and develop new types of ultra-high-temperature TBCs that can withstand more extreme thermal environments. Subsequently, this paper explains the core service mechanism of these advanced TBCs, which achieve synergy through two key approaches: reducing the thermal conductivity through phonon scattering and improving the thermal emissivity. It also analyzes the key damage mechanisms that threaten TBC longevity, including the growth of thermally grown oxide (TGO) at the coating interface, coupled corrosion caused by multiple factors, erosion-induced spallation, and sintering densification. This elaborates the innovation directions of high-entropy TBCs: the focus is moving toward multi-layered, gradient, and complex designs of the coating surface; the bond coat alloy is becoming more diversified and highly entropic through doping and dissolving refractory elements (such as W, Mo, and Ta) into its structure (to enhance high-temperature stability); and the top ceramic layer is undergoing structural diversification and high-entropy engineering based on classic structures such as fluorite, pyrochlore, and perovskite (to balance thermal insulation and corrosion resistance). Additionally, this review examines the application prospects of multi-principal component coating design driven by computational materials science, represented by machine learning, first-principles calculations, and phase diagram calculations, as well as the use of refractory high-entropy coatings under extreme operating conditions (such as hypersonic flight and nuclear energy systems). Finally, this paper proposes that developing new coating preparation technologies and combining them with existing mature ones while focusing on the efficient and low-cost preparation of high-entropy TBCs is the key path to the wide application of high-entropy coatings in hot-end component protection. This paper is expected to provide clear guidance for the development of high-performance coatings and contribute to the collaborative advancement of coating research and applications under harsh working conditions.

Copper-based powder metallurgy materials have emerged as attractive candidates for the brakes and clutches of high-speed trains, wind power yaw systems, mining trucks, and automobiles, owing to their good thermal conductivity, excellent wear resistance, and stable friction coefficient. However, the reliability and safety of equipment services have been drastically reduced by the increasingly harsh working environment, which is heavily influenced by the wear of copper-based powder metallurgy materials, functional degradation of parts, potential internal fatigue, and other problems caused by friction and vibration. Finally, friction-induced vibration and noise (FIVN) is triggered, a phenomenon that has puzzled researchers for several years. After years of sedimentation, although extensive research methods and theories related to FIVN have been developed, relevant research still needs to be pursued due to the arcane mechanism of its generation and the limited effectiveness of suppression methods. To address the severe challenges caused by friction and wear, innovations in surface texture technology, which play an increasingly important role in antifriction and antiwear applications, should be urgently developed to ensure the safe and reliable service of components. Considering that interface wear and debris rheology are the main culprits of the FIVN, a previous study found that a surface filled with gray iron HT300 could reduce interface wear, maintain the steady-state of the friction syetem, and effectively inhibit the generation of the FIVN. Therefore, to further explore the application scope of the surface filled with gray iron HT300 to reduce FIVN and fully reveal the mechanism of its interface tribological behavior is critical. In this study, the tribological performance of copper-based powder metallurgy materials is improved, and the design method for a surface filled with gray iron HT300 is further extended to a flat-to-flat contact configuration. First, grooves are machined on the surfaces of friction blocks made from copper-based powder metallurgy, and the grooved blocks are then filled with gray cast iron (HT300) to obtain three types of samples with different surface characteristics: original friction blocks, grooved friction blocks, and friction blocks filled with gray cast iron. Tribological tests are then performed on friction block samples with different surface characteristics and friction disc samples in a flat-to-flat contact configuration. By combining finite element simulations and numerical analyses, the synergistic effects of surface grooves and gray cast iron on the frictional behavior of copper-based powder metallurgy materials are thoroughly explored. Based on signal processing, micromorphology analysis, and theoretical analysis, the results show that copper-based powder metallurgy friction blocks with different surface characteristics exhibit varying wear properties and interface contact states, ultimately leading to different system responses. Compared with the original and grooved friction blocks, the friction blocks filled with gray cast iron significantly increased the contact area at the disc-block interface. They expanded the contact area, thereby alleviating stress concentration and effectively improving interface wear. Compared with the original and grooved friction blocks, the friction blocks filled with gray cast iron significantly enhance the disc-block interface contact degree and expand the contact area, thereby alleviating stress concentration and effectively improving the wear state at the interface. Additionally, the friction blocks filled with gray cast iron reduced the contact inclination angle at the disc-block interface, thus enhancing the system stability and effectively attenuating FIVN intensity. Therefore, an innovative surface design combining surface grooves with gray cast iron fillers meets the requirements for improving the tribological performance of copper-based powder metallurgy materials.

Diamond-like carbon films that exhibit exceptional properties including high hardness, low friction factor, wear resistance, corrosion resistance, and good biocompatibility, making them a valuable tool for coating tools, automotive parts, biomedicine, and other fields. Physical vapor deposition (PVD) is one of the most common techniques used to deposit diamond-like carbon films. However, the characteristics of carbon films produced by different PVD techniques exhibit notable disparities that constrain their applicability in industrial contexts. To address this issues, this study summarizes the research progress in the preparation of diamond-like carbon films using PVD technologies and the current improved technologies that have been developed in response to the poor comprehensive mechanical properties of carbon films caused by large droplets during the deposition of DLC films using CAE technology. These include imposed pulse cathode arc evaporation, filtered cathodic vacuum arc, pulsed laser-induced cathodic vacuum arc, and thermoionic vacuum arc technologies. To address the challenges posed by HiPIMS technology in an Ar atmosphere, such as the inability to effectively ionize the graphite target and the resulting low hardness and density, novel technologies have been developed to enhance the performance of carbon films by modulating the sputtering gas and optimization of the discharge process of the power supply. These techniques include short-pulse HiPIMS, deep oscillation magnetron sputtering, mixed-mode HiPIMS, and bipolar HiPIMS. Using short-pulse HiPIMS, deep oscillation magnetron sputtering, and mixed-mode HiPIMS technologies has been demonstrated to enhance the ionization rate of graphite targets. Furthermore, bipolar HiPIMS improves the efficiency of carbon ion transport. A comparative analysis of the properties, advantages, and disadvantages of DLC films deposited using these techniques was conducted to evaluate their application potential. In addition, research progress on the adhesion, tribological, and multi-factor coupling properties of diamond-like carbon films is summarized. In the following discussion, the efficacy of elemental doping and multilayer composite structures for enhancing the performance of DLC films in diverse service environments is examined. Patterning DLC films with different segmented structures is a novel technique for enhancing the tribological properties of carbon films. The current state of DLC films in engineering applications is introduced, and the structural and performance requirements of DLC films in different application scenarios are summarized. Finally, the new PVD technologies are compared for the above application scenarios. Tool coating represents a prevalent application domain for DLC films. However, the wear of carbon films at elevated temperatures and low bond strength represent pressing challenges to be addressed in the large-scale production and application of DLC tool coatings. In contrast to conventional nitride and carbide ceramic films, DLC films enhance the corrosion resistance and conductivity of metal bipolar plates in fuel cells, indicating their promising application in fuel cell bipolar plate coatings. The preparation of diamond-like carbon films using PVD technology is a promising future path, and the emerging HiPIMS and its improved technology can provide a cost-effective coating solution that is well suited for industrial applications. Nevertheless, there remains a significant disparity between our high-performance DLC film deposition technology and equipment, and advanced international standards. In addition, exploring coupled damage and detection methods in various complex environments is a promising avenue for future research. This study presents a comprehensive review of the development status and trends in diamond-like carbon films prepared using PVD technology aiming to establish a foundation for developing cost-effective, high-performance DLC technologies better suited for industrial applications.

With the progress of science and technology and improvements in living standards, the demand for electronic equipment has gradually changed from rigid and bulky to flexible and lightweight. Consequently, flexible electronic devices have become increasingly popular. Flexible wearable electronic devices are the development and innovation of flexible devices and have gained wide attention in the fields of healthcare, motion tracking, and environmental monitoring owing to their advantages such as light weight, portability, high integration, and good shape preservation. However, the long-term stability of wearable devices is challenged by their complex working environments, both from the external environment and secretions of human skin (rain, sweat, food residue, etc.). Inspired by the special biological surfaces in nature, the realization of special functions of materials or devices by regulating surface wettability has become a research hotspot. Surface wettability regulation has significant advantages for optimizing the design of solid-liquid interface interactions. Because liquid droplets can form spheres and quickly roll off, superhydrophobic surfaces have versatile functionalities such as waterproofing, self-cleaning, anti-corrosion, and antibacterial properties. This provides new opportunities to improve the performance and prolong the life of wearable electronic devices. For example, its excellent waterproof function can prevent external moisture intrusion, reduce the risk of short circuit and corrosion, and extend the service life, thus ensuring the stable operation of the device in wet environments. Self-cleaning and anti-contamination properties can keep the device clean, ensure accurate signal transmission and stable performance, eliminate the hassle of frequent cleaning, and improve the user experience. In addition, the superhydrophobic surface can reduce liquid accumulation, maintain device cleanliness, and improve comfort levels, laying the foundation for the wide application of superhydrophobic surfaces in flexible wearable electronics. This study focuses on the application of superhydrophobic surfaces in flexible wearable devices. First, the working principle of a superhydrophobic surface is introduced. The key to obtaining a superhydrophobic surface is to reduce the surface energy and increase the surface roughness. The preparation methods for superhydrophobic surfaces, including electrochemical deposition, electrospinning, chemical vapor deposition, and etching, are briefly described. This is followed by the application of superhydrophobic surfaces in flexible electronic devices. First, the application of superhydrophobic coatings in sensors is introduced. When a superhydrophobic coating is applied in the microchannel modification of a sweat sensor, the sweat transfer rate is significantly increased; thus, the sensing performance is improved. Superhydrophobic surfaces can provide sensors with moisture resistance, liquid resistance, self-cleaning, and weather resistance properties, significantly improving their service life. Second, the applications of superhydrophobic coatings in energy-conversion devices (such as nanogenerators) are described. Because the working principle of friction nanogenerators is to collect the electrostatic energy generated by contact charging, the waterproofing performance of the superhydrophobic coating helps friction nanogenerators collect more energy from the flowing water. Subsequently, the application of superhydrophobic coatings to energy-storage devices that provide energy support for flexible wearable electronic devices is introduced. Superhydrophobic coatings can significantly improve the safety and stability of energy storage devices. Although superhydrophobic coatings have certain applications, their service stability still faces challenges. Finally, it is pointed out that high mechanical stability, good environmental durability, and high light transmittance are challenges for the future development of superhydrophobic surfaces for wearable devices.

Overlaying and thermal spraying, core technologies in modern material surface engineering, have been indispensable in industrial manufacturing and equipment restoration since the 20th century. However, accelerated industrialization has imposed increasingly stringent demands on material surface properties—such as wear resistance, corrosion resistance, and high-temperature resistance—in sectors including machinery, energy infrastructure, and aerospace, exposing the limitations of conventional overlaying and thermal spraying techniques in addressing material protection and functional enhancement under complex operational conditions. By reviewing the integration and evolution of overlaying technology within surface engineering, this article highlights key advancements and applications in both fields over the past decade while outlining their developmental trajectories. Technological advancements in materials, processes, and equipment in the field of overlaying technology have been systematically summarized using various methods. These include arc surfacing techniques, such as shielded metal arc surfacing, submerged arc surfacing, gas metal arc surfacing, self-shielded arc surfacing, tungsten inert gas surfacing, and cold metal transfer surfacing; high-energy beam surfacing approaches like plasma arc surfacing and laser cladding; and specialized surfacing technologies such as oxy-acetylene surfacing. Although traditional high-chromium iron-based wear-resistant flux-cored wires remain mature for engineering applications, recent efforts have prioritized cost-effective high-boron iron-based alternatives. Nickel-based, cobalt-based, and metal-ceramic composites continue to dominate material research, with high-entropy alloys (HEAs) emerging as focal points in laser cladding. Process studies emphasize the optimization of parameters such as current, speed, and powder / wire feeding rates, along with auxiliary techniques such as ultrasound, magnetic fields, and heat treatment, to enhance the layer microstructure and performance. Advancements in overlaying equipment have primarily focused on enhancing the efficiency, quality, and precision of the surfacing processes. Additionally, the article provides a detailed overview of the practical implementation of surfacing technology across industries such as petrochemicals, cement and mining, metallurgical and power generation, agricultural and forestry machinery, aerospace, medical devices, and nuclear energy. Current research in the field of thermal spraying focuses on technologies such as cold spraying, plasma spray-physical vapor deposition, suspension plasma spraying, and detonation spraying, each with distinct priorities. Cold spraying focuses on theoretical research, development of high-performance equipment, standardization of raw materials, and optimization of coating performance. Plasma spray physical vapor deposition concentrates on optimizing process parameters, such as powder feeding rate, plasma gas composition, and spraying distance, to regulate coating growth patterns and microstructures with the aim of achieving high-performance coatings. Suspension plasma spraying explores the fabrication of high-performance thermal barrier oxide ceramic coatings. The development of high-frequency focused-energy detonation spraying technology has resulted in an order-of-magnitude improvement in efficiency and significantly enhanced coating quality. Additionally, the applications of thermal spray coatings, including wear resistance, thermal barriers, corrosion resistance, and functional coatings, are summarized. Regarding the future development trends of overlaying and thermal spraying technologies, it points out that high-end equipment overlaying materials, composite overlaying technology, as well as the automation, intelligence, and flexibility of overlaying processes will be the future development directions for overlaying technology. For thermal spraying technology, the development of new materials, novel processes, and improvements in the coating density remain key advancement priorities. These findings provide theoretical support and directional guidance for the technological evolution and industrial applications of overlaying and thermal spraying technologies.

45CrNiMoVA high-strength steel is widely used in manufacturing the torsion shafts of armored vehicles owing to its high strength, high toughness, high plasticity, and excellent fatigue resistance. However, it was suffered from stress corrosion cracking in corrosive environments; to address this issue, protective coatings are typically applied to the substrate surface to extend the service life of the components. In this study, an iron-based coating was prepared on the surface of 45CrNiMoVA high-strength steel using (by) laser cladding technology, and the coating surface was strengthened using ultrasonic impact treatment (UIT). Currently, research on the changes in microstructure and mechanical properties of high-hardness coatings after ultrasonic impact is limited, with most studies focusing on coatings with hardness below 600 HV_0.1. The objective of this study was to investigate the strengthening effect of UIT on high-hardness coatings and explore the combined effect of laser cladding and UIT on the strengthening of high-strength steel components. A laser confocal microscope was used to determine the surface roughness values of the coatings before and after UIT. The phase compositions and cross-sectional microstructures of the coatings before and after UIT were observed by X-ray diffraction analysis and optical microscopy. The residual stress values of the coating before and after UIT were measured using an X-ray stress analyzer. The microhardness of both types of coatings was tested using a Vickers microhardness tester. Electrochemical corrosion tests were conducted on the substrate and the coating (both before and after UIT) in 3.5wt.% NaCl solution using a three-electrode system electrochemical workstation. The results is showed that the surface roughness of the iron-based coating reached 12.76 μm. After UIT, the peak-shifting and valley-filling effects induced by surface plastic flow made the surface smoother and reduced the surface roughness to 2.05 μm (83.93% reduction). The iron-based coating primarily consisted of equiaxed grains, dendrites, and columnar grains. After UIT, an impact layer of thickness ~15 μm was formed on the surface, with grain fragmentation, compression, and elongation observed in the surface layer, along with plastic flow along the processing direction. The grain density increased; however, no significant grain changes were observed in the subsurface or interior of the coating. After UIT, the coating surface transformed from the Fe-Cr phase to a mixture of Fe-Cr and Cr0.19Fe0.7Ni0.11 phases. The (110) diffraction peak shifted to the right and its width increased, indicating grain refinement and the presence of residual compressive stress. The stress state of the coating after UIT changed from residual tensile stress (97 MPa) to residual compressive stress (-200 MPa). The maximum residual compressive stress was observed at the surface, and the residual compressive stress gradually decreased along the depth of the coating. Hardness testing was revealed that the maximum hardness at the top increased from 772 HV_0.1 to 889 HV_0.1. Because of the greater hardness of the coating, its resistance to plastic deformation was strong. After UIT, the coating hardness significantly increased within a 100-μm distance from the surface, with the improvement effect gradually weakening along the depth. The substrate exhibited poor corrosion resistance, the coating potential shifted positively by 130 mV after UIT, and the self-corrosion current density decreased by 56.48%. The reduced surface roughness, grain refinement, work hardening, and the presence of residual compressive stress on the UIT-treated coating hindered the infiltration of corrosive ions, making the coating more resistant to corrosion in the 3.5wt.% NaCl solution. Therefore, the process adopted in this study helped overcome the difficulties associated with surface strengthening of traditional hard coatings and provided a reference for future research and application of laser cladding and UIT for high-hardness coatings.

Ultrahigh-temperature boride-silicon carbide-based ceramics are highly promising thermal-protection materials for the thermal components of high-speed aircraft owing to their high melting point, excellent thermal conductivity, and superior ablation resistance. This review systematically summarizes recent studies pertaining to the oxidation and ablation resistance of ultrahigh-temperature boride-silicon carbide coating materials. It focuses on the enhancement mechanisms achieved by incorporating various modification phases, including refractory metal silicides, rare-earth oxides, and other additives, such as borides, carbides, oxides, and metallic / non-metallic elements. The incorporation of SiC as a second phase significantly enhances the oxidation and ablation resistance of ZrB₂ and HfB₂ ceramics. The formation of a SiO₂-rich glassy phase effectively prevents oxygen diffusion. However, in high-temperature environments exceeding 1 800  ℃, SiC undergoes active oxidation. This results in the formation of a porous SiC depletion layer, which severely degrades the oxidation and ablation resistance of the ultrahigh-temperature boride-silicon carbide coating material. To suppress this phenomenon, researchers have introduced various modification phases to improve the oxidation and ablation resistance by regulating the structure of the oxide scale, increasing the viscosity of the glass phase, and inhibiting oxygen diffusion. Refractory metal silicides (e.g., MoSi₂, WSi₂, TaSi₂, ZrSi₂, and HfSi₂) enhance the oxidation and ablation resistance by providing an additional Si source, thereby resulting in complex glass phases and promoting densification. MoSi₂ and WSi₂ form volatile MoO₃ and WO₃ during oxidation, thus reducing the surface temperature; however, their excessive addition increases porosity. The modifying effect of TaSi₂ exhibits significant temperature dependence. At an intermediate temperature (approximately 1 600 ℃), TaSi₂ effectively inhibits the formation of a SiC depletion layer. The oxidation product Ta₂O₅ dissolves in the glass phase or reacts with ZrO₂ / HfO₂, thus resulting in a denser oxide scale. At ultrahigh temperatures (>1 900 ℃), Ta-containing oxidation products have relatively low melting points and tend to form low-melting eutectic phases, thus reducing the stability of the oxide scale. ZrSi₂ and HfSi₂ enhance the stability of the oxide scale by forming (Zr,Hf)O₂ solid solutions, which inhibit oxygen diffusion. Rare-earth compounds (e.g., La₂O₃, Y₂O₃, Sm₂O₃, and Yb₂O₃) improve the oxidation and ablation resistance of coatings by refining grains, stabilizing ZrO₂ / HfO₂ structures, increasing the viscosity of the glass phase, and enhancing material emissivity. Rare-earth cations dissolve in the ZrO₂ / HfO₂ lattice, thus suppressing volume changes during phase transition. Additionally, La₂O₃ and LaB₆ facilitate the formation of a stable La-Si-O glass layer. Y₂O₃ can react with SiO₂ to form silicate nanocrystals, such as Y₂Si₂O₇ or Y₂SiO₅, which disperse in the glass phase and increase the viscosity. Sm₂O₃ significantly enhances the emissivity of the coatings, strengthens thermal radiation, and reduces the surface temperature. Yb₂O₃ effectively increases the viscosity of the glass phase owing to its small ionic radius and high field strength. However, excessive addition of rare-earth elements may weaken the glass-phase structure and increase the oxygen-vacancy concentration, thus weakening the oxidation and ablation resistance of the coatings. Other modification phases, such as borides (TaB and WB), carbides (ZrC, WC, and TaC), oxides (MgO and Al₂O₃), and metallic / non-metallic elements (W, Si, and C), can enhance oxidation and ablation resistance through different mechanisms. ZrC can occupy the pores by forming ZrO₂, which inhibits the formation of the SiC depletion layer. The oxidation of WC forms WO₃, which promotes the liquid-phase sintering of ZrO₂. Graphene modification significantly improves the thermal conductivity and reduces the surface temperature of the coatings. The introduction of elemental Si directly increases the Si content and suppresses the active oxidation of SiC. Currently, the thermal-protection performance of ultrahigh-temperature boride-silicon carbide coating materials is limited to 2 300 ℃. Future studies should focus on the following aspects: first, the dynamic evolution mechanisms and quantitative evaluation methods for oxide scales should be investigated comprehensively. Second, data-driven approaches can be used to screen for modification phases and predict material performance. Finally, new active-passive synergistic thermal-protection mechanisms must be identified.

Additive remanufacturing technology can be applied to directly form titanium alloy components. However, the mechanical properties of the as - deposited remanufactured components are either inferior to or only comparable to those of cast parts. This technology struggles to meet the emergency demand for direct deposition and immediate use in additive remanufacturing. A method of using pulsed plasma arc additive remanufacturing is studied to repair the surface of titanium alloys. To investigate the influence of different pulse frequencies on the microstructure and properties of deposited layers with different thicknesses, deposition experiments were conducted using pulse frequencies ranging from 1 to 100 Hz at intervals of 10 Hz. Single - pass single - layer and single - pass multi - layer specimens were deposited, and their microstructures and mechanical properties were analyzed. The influence of different thicknesses of pulsed plasma arc surface deposits on the microstructure and mechanical properties of remanufactured titanium alloy components was studied. The research results indicate that the surface roughness and hardness of the titanium alloy deposited by pulsed plasma arc are related to the cooling rate during deposition. A higher microhardness corresponds to a greater cooling rate, and the change rule of larger surface roughness is consistent with a higher cooling rate during deposition and solidification. Additionally, the distribution of hardness values at the bottom and top in the deposition direction is that the microhardness of the martensite structure > the grain boundary > the Widmanstätten structure with basket - weave characteristics. It can be inferred that the disturbing effect of the arc and droplet transfer enhances the cooling gradient during the solidification process, thereby affecting the surface roughness and microhardness. The microstructure of titanium alloy parts fabricated through pulsed plasma arc deposition is characterized by a composite structure composed of acicular martensite and Widmanstätten structure. During the deposition process, the perturbation effect of pulse frequency on droplet transfer plays a crucial role in promoting grain refinement. This is clearly demonstrated by the equiaxed grain structure observed in the first deposited layer. Pulsed plasma arc deposition was employed to fabricate multi - layer components. Subsequently, electron backscatter diffraction (EBSD) was utilized for phase analysis. The research results show that in the multi-deposited layer structure, the proportion of the α phase is 99.9%, and the proportion of grain size ≤ 15 μm reaches 86%. It can be seen that under the multi - layer thermal cycle, the decomposition of the metastable martensite structure in the deposition layer promotes the precipitation of secondary nano - α phase, further improving the interface strength of the mechanical properties of the titanium alloy repaired by plasma arc additive remanufacturing. Comparing the specimens with the substrate interface and the deposited layers, the former has higher tensile properties than the latter, and the mechanical properties under the 70Hz process reach the forging level, which is the best. Moreover, when comparing titanium alloy parts deposited at different pulse frequencies, the tensile strength of the as - deposited parts from high to low is 70 Hz > 50 Hz > 90 Hz. The reason is that the thermal cycle input of the 70Hz pulsed plasma is most conducive to maximizing the disturbing effect on the droplet transfer, resulting in the largest cooling gradient in the deposition layer of the pulsed plasma arc - deposited titanium alloy. Furthermore, due to the promotion of secondary nano-α phase precipitation by multiple thermal cycles, the mechanical properties of the components processed under this regime have been further enhanced. The research on the pulse plasma arc additive remanufacturing method for titanium alloys can effectively improve the mechanical properties of the as-deposited state of components during online repair. This provides a theoretical and technical foundation for the repair of advanced equipment.

High-end equipment, such as aero-engines, gas turbines, and advanced CNC machine tools, plays a critical role in national defense and industrial sectors. These systems are characterized by their high technological complexity, long development cycles, diverse structural and functional requirements, and stringent service conditions. The development and iterative upgrading of such equipment are crucial for maintaining national strategic capabilities and require extensive interdisciplinary, inter-industry, and inter-regional collaboration. As a core aspect of full life-cycle management, remanufacturing high-end equipment offers significant economic and strategic benefits. It effectively reduces costs, extends service life, and facilitates generational equipment upgrades, capabilities essential for keeping pace with technological advancements and maintaining competitive advantage across industries. In this study, aero-engines are used as a representative case to analyze the value chain activities involved in high-end equipment remanufacturing. The research identifies several key challenges, including complex coupling between design and manufacturing interfaces, insufficient information sharing, and a disconnect between knowledge accumulated during remanufacturing and its integration into the development of new models. These issues hinder the effective functioning of the remanufacturing value chain and limit its potential in terms of cost reduction, technological advancement, and sustainability. To address these challenges, this study proposes a comprehensive value-chain framework for high-end equipment remanufacturing, organized across four dimensions: “value chain entities, value activities, full life cycle of development, key technology support”. This framework offers a systematic approach to organizing and optimizing collaboration among stakeholders, including design institutes, manufacturers, suppliers, users, research institutions, and remanufacturing enterprises, across different stages of the equipment life cycle, spanning from design and manufacturing to maintenance and remanufacturing. The framework is supported by four key technology pillars: data intelligence, process intelligence, platform intelligence, and agile intelligent systems engineering. Data intelligence ensures continuous data flow and accurate feedback throughout the equipment life cycle. Constructing a multimodal closed-loop data system enables the creation of a high-fidelity digital twin, thereby facilitating real-time decision-making and information sharing. Process intelligence enhances this process by enabling the reconstruction and dynamic optimization of business processes through cross-stage modeling and self-learning algorithms. This allows for the continuous improvement of processes throughout the life cycle of the equipment, moving beyond simple repair and towards a more comprehensive system optimization. Platform intelligence, supported by the Industrial Internet, optimizes multi-stakeholder collaboration by enabling role allocation, dynamic incentives, and seamless resource and data sharing. It provides a common platform for all participants to interact and share resources and data, ensuring efficient coordination and collaboration among manufacturers, suppliers, users, and research institutions. Agile intelligent systems engineering ensures that the system can dynamically adapt to evolving conditions through interdisciplinary simulation and iterative optimization, enabling rapid responses to unforeseen challenges and technological demands. Implementing this remanufacturing value chain framework reduces total life-cycle costs, extends equipment service life, and enables the restoration of equipment to better than new condition. It also facilitates generational upgrades of high-end equipment, thereby enhancing resilience and self-controllability across the industrial chain. The integration of artificial intelligence with high-end equipment remanufacturing is expected to drive the development of advanced, adaptive, and sustainable manufacturing systems. Despite these benefits, several challenges remain, including limitations in organizational incentive mechanisms, barriers to data interconnection and sharing, and insufficient model interoperability across different stages and sectors. Future research should focus on developing demonstrative cross-domain collaboration models, standardizing data-sharing protocols, and improving organizational structures to promote high-quality development in the high-end equipment remanufacturing industry. Addressing these challenges will help fully realize the potential of the proposed value chain framework and advance global manufacturing technology.

The surface treatment of titanium alloy fasteners is one of the main methods for preventing “sticking” and “biting” during assembly and disassembly. It is necessary to investigate the frictional and wear characteristics of titanium alloy samples after different surface treatments, reveal their wear mechanism, and improve the tribological properties of their surfaces. In addition, it is crucial to reduce the factor of friction, improve wear resistance, and design highly reliable titanium-alloy fasteners. In this study, a manual-spraying method was developed for applying aluminum and MoS₂ treatments to samples after pulse-anodizing treatment (PA) to leave the surface untreated. Four surface states of TC4 titanium alloy (no treatment [LT], pulsed-anodizing treatment, pulsed-anodizing and aluminum-coating composite treatment [PA-Al], and pulsed-anodizing and molybdenum disulfide composite treatment [PA-MoS₂]) were investigated, and a 10-mm-diameter TC4 titanium alloy ball was used as the grinding object. The frictional and wear characteristics of TC4 titanium alloys in different surface states were determined under 1 and 4 N loads using a UMT-3 friction- and wear-testing machine. The wear morphologies of the wear marks and wear spots on the surface of the ball were characterized using an ultradepth field microscope, a three-dimensional white-light interferometer, a focused-ion beam scanning electron microscope, and an accompanying energy dispersive spectrometer. The wear volume and wear rate were calculated to determine the differences in wear resistance, examine the wearing mechanism, and analyze the differences in wear resistance under different test loads. Under test loads of 1 and 4 N, the wear marks of the LT sample are the widest and deepest, the factor of friction fluctuates significantly with an average value of approximately 0.53, and the main element is Ti. In addition, Al, V, O, and C are observed, and the wear mechanisms are mainly plowing and adhesive wear. The wear morphology of the PA-Al sample shows discontinuous spalling, the factor of friction fluctuates slightly, and the stability value is approximately 0.58. More Al and O elements are observed on the surface of the sample, and alumina is formed on the surface, indicating high hardness and brittleness; thus, the sample is prone to brittleness. Spalling pits are formed on the surface, effective solid lubrication films rarely form on the surface of the sample, the run-together period is extended, and the coefficient of friction is high. The wear mechanisms of the PA-Al sample are spalling and abrasive wear. The wear marks on the PA-MoS₂ samples are shallow and continuous, the factor of friction fluctuates slightly, the stability value is approximately 0.25, and the main elements are S and Mo, with low amounts of C, O, and Si. Relatively dense TiO₂ coatings are generated on the surface of the PA sample, indicating high hardness, good antifriction, and high bonding strength with the substrate; therefore, the wear resistance of the material improves significantly. The wear mark of the PA sample is the narrowest, and the factor of friction is approximately 0.16. The wear rates under the low and high loads are 5.8×10^-4 and 5.7×10^-4 mm³ / (N·m), respectively, indicating that the sample exhibits the best wear resistance. Its main elements are Ti and O, with low amounts of Al, C, P, and Mo. The wear rates of the samples are ranked from high to low as follows: PA-Al>PA-MoS₂>LT>PA. This demonstrates that the pulse-anodized-treated TC4 titanium alloy exhibits the best antifriction wear resistance, and the interlayer shearing force of MoS₂ on the surface of the PA-MoS₂ sample is small. This improves the lubrication characteristics; however, because it has a rough surface microstructure, the frictional resistance is the second best, and the wear resistance further decreases under a load of 4 N. This proves the significant advantages of PA in improving the antifriction wear resistance of TC4 titanium alloys and provides a strong technical support and experimental basis for the surface treatment of titanium alloy fasteners.

Remanufacturing has emerged as a critical strategy for resource recycling and promoting sustainable industrial production. In this context, microcrack detection in remanufactured blanks constitutes an essential aspect of quality control throughout the remanufacturing process, directly influencing the integrity, reliability, and service life of recycled components. This paper presents a systematic review of recent advances in active infrared thermography (IRT) as a nondestructive testing method for microcrack detection in remanufactured blanks. The fundamental principles of active IRT are introduced, emphasizing its capability for rapid, full-field, and noncontact inspection. The paper also provides a detailed analysis of the three predominant excitation mechanisms, namely eddy current, ultrasonic, and laser-based approaches, highlighting their respective physical principles, advantages, and limitations in the context of remanufacturing. Eddy current thermography is particularly effective for conductive materials, enabling high-speed scanning and surface crack detection; ultrasonic thermography excels in detecting subsurface defects through vibrothermal effects; and laser-based thermography offers superior resolution for precise characterization of fine surface cracks. In addition to excitation mechanisms, this review thoroughly examines advanced signal-processing techniques that are essential for enhancing defect visibility and interpretation. These include conventional image processing methods (e.g., Fourier transform and pulsed-phase thermography), data decomposition and dimensionality reduction approaches (such as principal component analysis and tensor decomposition), and emerging deep-learning-enabled intelligent recognition algorithms that improve automated flaw identification and classification. The performance of these techniques is discussed in terms of signal-to-noise ratio enhancement, defect contrast improvement, and computational efficiency. A comprehensive summary of applications and performance evaluations demonstrates the effectiveness of active IRT across various case studies involving remanufactured components. This paper further addresses persistent challenges that limit wider industrial adoption, including limited detection accuracy for microscale cracks, poor adaptability to complex and curved surfaces, susceptibility to environmental interference, and difficulties in achieving reliable quantitative characterization of crack dimensions and morphology. Several future research directions are proposed to address these challenges. Emphasis is placed on the development of intelligent signal processing frameworks that integrate real-time deep learning, multisensor data fusion, and adaptive noise suppression. The design of high-efficiency excitation sources aimed at improving the thermal contrast while reducing energy consumption is also discussed. Other promising research avenues include multiphysics coupling methodologies that combine thermal, ultrasonic, and electromagnetic stimulations for enhanced defect detectability, as well as digital-twin integration for virtual-physical system interoperability and predictive maintenance. Finally, the development of portable, cost-effective, and robust inspection systems tailored for in-situ remanufacturing environments is highlighted as a critical step toward field deployment. The results of this review demonstrate that active IRT offers considerable advantages and holds promise for accurate and efficient microcrack assessment in remanufactured components. With continued innovation and system integration, active infrared thermography is expected to provide robust technical support for quality enhancement and sustainable transformation in the remanufacturing industry.

Nano minimal quantity lubrication (NMQL) has become a research hotspot in the field of green manufacturing, which significantly improves the cooling, lubrication, and friction reduction properties of bio-lubricants. However, the stability of nanofluids, multi-field coupling mechanism and industrial applicability are still the key challenges limiting its wide application. This paper systematically reviews the latest research progress in NMQL, focusing on the preparation methods, physicochemical properties, and tribological behavior of nanofluids, along with their performance enhancement mechanisms under the coupling of electric, cryogenic, and magnetic fields. It is demonstrated that nanoparticles (e.g., MoS₂, graphene, Al₂O₃) contribute to reduced grinding temperatures and improved workpiece surface quality owing to their high thermal conductivity, extreme pressure anti-wear properties. Hybrid nanofluids further optimize the load-bearing capacity and thermal conductivity of the lubricating film through synergistic mechanisms. In addition, the introduction of multi-physical fields, such as magnetic field induced directional alignment of nanoparticles and regulation of fluid viscosity, electric and ultrasonic fields for enhanced droplet wettability, and cryogenic fields for suppressing grinding thermal damage provides new pathways for the precise regulation of NMQL performance. This paper also discusses challenges related to the sustainability, cost-effectiveness, and scalable application of NMQL, and proposes future research directions, including optimizing the long-term stability of nanofluids, developing intelligent adaptive lubrication systems, and elucidating multi-field coupling mechanisms. This review aims to provide theoretical support and technical reference for the engineering application of NMQL in efficient and green machining. Currently, most reviews on NMQL focus primarily on the physicochemical properties and mechanisms of nanofluids. There remains a lack of systematic analysis of the coupling mechanisms involving different physicochemical properties such as viscosity, surface tension, nanoparticle size, and shape of various nanojets under multi-field conditions, which hinders further development and application of NMQL technology. Current research in nanofluid minimal quantity lubrication is evolved from single-particle systems toward hybrid formulations and multi-field regulation strategies. In terms of nanoparticle selection, materials such as molybdenum disulfide, graphene, and aluminum oxide are demonstrated to be effective in reducing grinding temperatures and improving workpiece surface quality due to their high thermal conductivity and extreme-pressure anti-wear properties. These nanoparticles are widely recognized for their ability to form protective tribofilms on friction surfaces, thereby enhancing lubrication efficiency and wear resistance. Hybrid nanofluids, through synergistic interactions between different particle types, are employed to further enhance the load-bearing capacity and thermal conductivity of the lubricating film. The combination of different nanoparticles is often designed to leverage their complementary physical and chemical characteristics for optimal performance. Regarding performance modulation, multi-field intervention is shown to offer distinct advantages: magnetic fields are utilized to enable directional alignment of nanoparticles and viscosity regulation, electric and ultrasonic fields are applied to improve droplet wettability, while cryogenic fields are used to help mitigate grinding thermal damage. These approaches are regarded as new strategies for precisely controlling nanofluid performance. Nevertheless, key challenges are still required to be addressed, including ensuring long-term nanofluid stability, developing intelligent adaptive lubrication systems, and clarifying multi-field coupling mechanisms. These aspects are discussed in this review to provide theoretical guidance and technical support for the engineering application of NMQL in efficient and sustainable machining processes.

Current-carrying friction pairs are critical components in high-end applications such as motors, rail transit, and aerospace systems. These components serve dual functions: transmitting electrical energy and sustaining mechanical friction. Consequently, their reliability is essential to overall system performance. One key factor affecting their performance is current polarity, which significantly affects overheating, arcing, and surface degradation. This study investigates the causes and consequences of polarity effects through field investigations of carbon brush-collector ring systems in hydroelectric generators, supported by failure case analyses and theoretical frameworks. It was found that current polarity primarily governs the oxidation and transfer of surface films at the contact interface of current-carrying friction pairs, thereby regulating the physical and chemical properties of these films. In particular, polarity influences the growth of oxide layers and electrochemical reactions within the water film at the interface—a phenomenon broadly classified as anodic oxidation (AO). Material transfer from the anodic to the cathodic friction pair is attributed not only to arc-induced material migration but also to anodic oxidation mechanisms. For instance, in the carbon brush-steel slip ring system, the negative slip ring (acting as the anode) displayed more intense surface oxidation, forming a film primarily composed of metal oxides. Conversely, the positive slip ring (acting as the cathode) exhibited suppressed oxidation, with a surface film dominated by carbon-transfer deposits. These findings clearly demonstrate the strong influence of current polarity on surface film formation. Further analysis revealed a significant asymmetry in contact resistance under different polarities. This variation is attributed to the distinct surface film compositions and their associated conduction mechanisms. Additionally, current polarity impacts contact temperature, which in turn affects the thermal stability of the friction pair. By integrating case studies, the research systematically examines the interrelationships among contact resistance, localized temperature rise, and arc generation—placing particular emphasis on the severe damage caused by surface arcing. The results indicate that arc erosion characteristics are closely tied to current polarity. Specifically, anodic current-carrying components are more susceptible to thermal erosion, including melting and evaporation—an effect collectively referred to as “anodic evaporation”. This study provides a comprehensive analysis of the fundamental mechanisms, contributing factors, and final manifestations of polarity effects. It explores how polarity governs surface film formation, how these films affect contact resistance and temperature, and how these factors collectively affect arc probability and surface degradation. The interplay among surface films, temperature rise, and arc formation is examined in detail. Focusing on the carbon brush-steel slip ring system, the study highlights differences in wear and surface damage under opposing polarities, explaining the severe erosion of negative slip rings and abnormal wear on negative carbon brushes. Based on these findings, a mitigation strategy is proposed: reducing temperature through optimized cooling structures to interrupt the positive feedback loop between heat buildup and arc formation. Finally, the study summarizes the intrinsic mechanisms underlying polarity effects in current-carrying friction pairs, using the carbon brush-steel slip ring system as a representative case. It introduces the principle of “anodic protection” to provide both theoretical support and practical guidance for the optimal design, long-term reliability, and maintenance of such systems. Ultimately, this study aims to deepen the understanding of polarity effects on surface film formation, interface degradation, and system performance, while offering new insights for future research in this field.

Titanium alloy blades and engine cases experience local temperature increases under extreme conditions, such as impact and friction, causing titanium alloy parts to catch fire. The NiCrFeAl / BN thermal insulation flame-retardant coating can effectively prevent the occurrence of titanium fires. Preparing thermal insulation and flame-retardant coatings on the surface of titanium alloys is crucial to prevent titanium fires. The thermal insulation effect and crack propagation of the NiCrFeAl / BN flame-retardant coating during thermal shock cycles have not been thoroughly studied. The temperature and stress distribution of the coating system with NiCrFeAl / BN as the thermal insulation layer, YSZ as the flame-retardant layer, and NiCoCrAlY as the bonding layer during the thermal shock cycles were simulated using the finite element method, and the development process of cracks during the thermal shock cycle was studied. A thermal-mechanical coupled two-dimensional finite element model of the coating system was established to study the temperature and stress changes of the coating and substrate during the thermal cycles. The crack initiation and propagation model was built by combining the extended finite element method (XFEM) and cohesive element. Using this combined model, the initiation and propagation behavior of the surface crack, internal crack, and interface crack in the coating system was simulated. The conventional finite element method must reconstruct the mesh when solving crack propagation problems, which limits its application. The XFEM uses extended shape functions to describe discontinuous displacement fields, which have significant advantages in simulating crack propagation without updating the mesh model. XFEM allows cracks to propagate freely under stress, rather than being forced to propagate along grid boundaries, and can penetrate the grid during propagation. Therefore, the Abaqus software XFEM was used to study the initiation and propagation of vertical cracks. The four materials of the substrate and coatings are divided into four cross-sectional zones. Each layer, from bottom to top, is as follows: a titanium alloy TC11 substrate with a thickness of 10 mm, a NiCoCrAlY metal bonding layer with a thickness of 0.15 mm, a YSZ ceramic thermal insulation layer with a thickness of 0.2 mm, and a NiCrFeAl / BN sealing surface layer with a thickness of 1.2 mm. In the alternating cold and hot environment, thermal stress is generated inside the coating. When the thermal stress accumulates to a certain degree, the coating may crack. Based on the actual thermal cycling experiment process of the coating sample, a transient analysis of the thermal coupling of the sample model is performed to simulate the cyclic process of the coating from heating to the insulation stage and then to water cooling. The temperature is raised from 20 ℃ to 750 ℃ within 15 s, maintained at 750 ℃ for 300 s, and finally cooled from 750 ℃ to 20 ℃ by water cooling within 30 s, which is considered as one cycle. A small crack is pre-set on the surface of the coating. During the first heating and insulation stage, the crack in the coating does not propagate. However, during the cooling stage, stress concentrates at the crack tip. When the stress reaches the failure criterion, the crack begins to increase along the direction of maximum stress. In the subsequent thermal cycle, the vertical crack continues to propagate, and if the coating is subjected to sufficient thermal stress, the vertical crack may penetrate the coating. With the increase in thermal shock cycles, the initial microcracks gradually spread to the interior of the coating and gradually approach a state of stability. When subjected to 400 cycles of water cooling and heating, no interface cracks appear between the coating and the substrate, and the maximum stress occurs at the interface between the coating and the substrate. After 543 thermal cycles, interface cracks are observed, starting from the vicinity of the NiCoCrAlY bonding layer and extending horizontally. At this point, stress is redistributed, and the cracked coating is nearly free from the influence of stress. The substrate is subjected to significant stress, and the evolution of interface cracks ultimately led to coating peeling and failure.

Ceramic matrix composites, characterized by high hardness, high brittleness, and poor material consistency, are widely used in the manufacture of key components, such as radomes in the aerospace industry. During machining, material properties lead to high cutting temperatures and significant vibrations, which can easily cause tool wear and undermine the processing quality and production efficiency of the products. Current research has primarily focused on metal material processing, and there has been relatively little research on tool wear prediction in composite material processing, particularly in ceramic matrix composite material machining. This study focuses on special ceramic matrix composites, collecting and analyzing tool cutting vibration signals during machining, and establishing models to predict tool wear. First, a ceramic matrix composite cutting tool wear prediction framework based on the cutting vibration was designed. Under this framework, cutting vibration data processing and tool wear prediction are at the core and receive data from machine tools and smart tool holders. Time-frequency domain feature extraction, correlation analysis, and feature extraction processing of the cutting vibration data were performed. Furthermore, a gated recurrent neural network was used to train a tool wear prediction transfer function model, thereby achieving tool wear prediction and analysis. Based on the prediction and analysis results, control of the tool change and machine start-stop was implemented. Second, through Spearman’s correlation coefficient analysis of the time-frequency domain feature data, the time-domain average and minimum values showed no significant correlation with tool wear, whereas the center of gravity frequency showed a significant negative correlation with tool wear, indicating that as tool wear intensifies, the low-frequency vibration induced by spindle rotation becomes more severe, and the remaining data showed a significant correlation with tool wear, with significance levels above 99%. It can be concluded that there is a significant correlation between the cutting vibration and tool wear data. Utilizing the time-frequency domain characteristics of the cutting vibration data can effectively guide tool wear prediction and cutting parameter optimization. Ceramic matrix composite samples were then used as test objects for the research. Orthogonal experiments were conducted to elucidate the influence of various factors on the cutting force and vibration, determine the main influencing factors, and select the optimal parameter combination. Through orthogonal experiments and range analysis, the optimal parameter combination for balancing tool life and processing vibration was determined: cutting width of 1.0 mm, cutting depth of 1.0 mm, spindle speed of 1 600 r / min, and feed rate of 2 400 mm / min. Single-factor experiments were conducted with the optimal cutting parameter combination to provide data support for the subsequent tool wear prediction analysis. Subsequently, a prediction model for tool wear was established based on a gated recurrent unit network. The model was trained using cutting data, and a real-time prediction evaluation of tool wear was conducted based on the measured operating condition data and mean squared error (MSE). Finally, the optimal validation MSE of the model was 68.528 2, and the prediction error conformed to a normal distribution with a mean of 0. The regression value R approached 1, indicating the effectiveness of the prediction model. Another set of tools was used to conduct cutting experiments with the same process parameters, obtaining 83 sets of time-frequency domain feature data. These 83 datasets were used as validation data for input into the tool wear prediction model, outputting the predicted tool wear values. The curves of the predicted and actual values were plotted, and the predicted curve aligned well with the actual curve. The prediction error range was -39.652 4 to 66.974 6 μm, indicating the model’s effectiveness under real data. In summary, the proposed method provides a theoretical and technical foundation for improving the processing quality and reliability of ceramic matrix composite products.

Medical-grade 316L stainless steel is widely used in artificial joint implantation, cardiovascular disease treatment, and various surgical tools owing to its excellent mechanical properties and easy processing and shaping. However, 316L stainless steel is prone to pitting corrosion in the complex fluid environment of the human body, thereby leading to inflammation and implant failure. In addition, its surface wear resistance is poor, and long-term wear further exacerbates the degradation of its surface properties. Depositing wear- and corrosion-resistant coatings, such as diamond-like carbon (DLC) coatings, on the surfaces of these components is one of the effective ways to solve this problem. Arc-enhanced glow discharge (AEGD) technology, which is a new technology developed in recent years, is generally used for ion sputtering and cleaning of the substrate/workpiece surface before coating. In this study, AEGD was used as an ion source by introducing a carbon-containing gas, thereby generating a carbon-containing plasma, which was then deposited onto the substrate surface to form a hydrogen-containing DLC coating. Using methods such as scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy, nanoindentation, friction and wear testing, and electrochemical testing, the effects of deposition temperature on the coating structure, mechanical properties, friction properties, and corrosion resistance were studied. M2 high-speed steel and 316L stainless steel were selected as the base materials for the experiment, with dimensions of Φ 20 mm × 3 mm. After grinding with sandpaper and mirror polishing, all the base materials were ultrasonically cleaned in acetone and anhydrous alcohol solutions for 15 min, then dried, and placed on the workpiece table of the coating equipment. The target material was high-purity Cr. When the vacuum chamber was heated to 170 ℃, the AEGD ion source was turned on, and high-purity argon gas was introduced at a pressure of 0.4 Pa. A DC bias of -200 V was applied to the substrate, and high-energy argon ions generated by AEGD were used to bombard and sputter the substrate surface to remove the oxide layer and pollutants on it. The objective was to improve the film/substrate bonding force and further enhance the bonding force between the DLC coatings and steel substrate. Before depositing a coating, a Cr bonding layer and CrC transition layer were deposited on the substrate surface using a Cr target. Then, in order to investigate the effects of deposition temperature on the structure and properties of DLC coatings, the vacuum chamber temperatures were controlled at 170, 250, 350, and 450 ℃, respectively, and the coating time was 60 min. The results showed that the DLC coatings prepared at different deposition temperatures generally exhibited smooth and flat surfaces. Using high-magnification SEM, no macroscopic particles were observed in the coatings prepared at lower deposition temperatures (170 ℃), and the surface roughness was lower. The coatings prepared at higher deposition temperatures (250, 350, 450 ℃) had macroscopic particles and higher surface roughness. This indicates that a lower-deposition-temperature preparation process suppresses the problem of large particles caused by “target poisoning” and can achieve a regular surface morphology. The content of sp³ hybridized bonds in the internal structures of the DLC films prepared at lower deposition temperatures was high. As the deposition temperature increased, the content of sp³ hybridized bonds gradually decreased, thereby leading to graphitization. The coating prepared at a deposition temperature of 170 ℃ exhibited excellent mechanical properties, with the hardness and elastic modulus reaching maximum values of 61 GPa and 414 GPa, respectively. The hardness remained around 10 GPa under other temperature parameters. In addition, the wear resistance of the coating prepared at 170 ℃ was improved, and its wear rate was reduced by six times compared with that of the substrate. The coating prepared at 250 ℃ had the best corrosion resistance, and its self-corrosion current density was reduced by about eight times compared with that of the stainless steel substrate.

Titanium alloys have excellent physical and mechanical properties and are widely used in many industries; however, their poor machinability not only reduces the machining efficiency but also the surface integrity, thus significantly decreasing the fatigue life. Based on the electroplastic effect and sliding electric-contact principles, electric pulse-assisted cutting can effectively reduce the workpiece strength and improve the tribological behavior between tool-chip / workpiece interfaces during cutting, thus significantly improving the machinability of metal materials to enhance the surface integrity of the workpiece. However, research on the fatigue performance of titanium alloys based on electric pulse-assisted cutting is insufficient. Considering the high-fatigue requirement of machined titanium-alloy components, this study performed electric pulse-assisted cutting on titanium alloys to investigate their surface integrity after they were subjected to electric pulse-assisted turning. A surface roughness tester, Vickers microhardness tester, scanning electron microscope, and electron backscattered diffraction system were used to characterize the workpiece surface roughness, surface morphology, surface work hardening, surface microstructure, and surface thickness of the plastic-deformation layer. Workpiece surface defects, including bonding, tearing, and tool marks, were significantly eliminated; the Vickers hardness reduced with increasing pulse-current parameters; and severe plastic deformation occurred on the workpiece surface along with significant grain refinement. Compared with the results of conventional dry turning, the surface roughness and work hardening of TC4 titanium alloy subjected to electric pulse-assisted turning decreased by 35.7% and 4.7%, respectively; the thickness of the strengthening layer increased by 2.14 times; and more α phases were changed to the β phase in the workpiece strengthening layer. The fatigue performance of the TC4 titanium alloy subjected to electric pulse-assisted turning was investigated using a fatigue-testing machine and scanning electron microscope. The fatigue life of the workpiece machined via electric pulse-assisted turning reached 528.18 × 10⁴ cycles, whereas that achieved via conventional turning was only 35.35 × 10⁴ cycles, thus signifying an improvement by 14.9 times. The fracture morphology of the fatigue specimen was observed using a scanning electron microscope. Fatigue cracks primarily originated from the machined workpiece surface owing to surface defects and stress concentration, whereas they were transferred from the surface to the subsurface in the machined workpiece, which resulted from the low surface roughness, smooth surface morphology, small surface work hardening, and large thickness of the plastic-deformation layer. In particular, the electroplastic effect accelerated dynamic recrystallization and reduced the dislocation density, thereby better coordinating the strain of the plastic-deformation layer on the machined-workpiece surface. Numerous fatigue striations were observed microscopically in the crack-propagation region. The fatigue striations were primarily formed by repeated sharpening and passivation of the crack tip under cyclic compressive and tensile stresses, and the direction of the fatigue striations was perpendicular to the crack-propagation direction. Each fatigue striation was equivalent to one cycle of load or strain, and the fatigue-striation width was closely related to factor such as the workpiece surface roughness, work-hardening rate, and microstructure. The fine grains, small dislocation density, and large plastic-deformation depth might have reduced the fatigue-striation width, thus hindering fatigue-crack propagation. The fatigue-striation width resulting from electric pulse-assisted turning was less than that yielded by the conventional turning. The fatigue-striation width at 50 ℃-0.4 A / mm²-500 Hz was 0.194 μm, which was 78.7% lower than that yielded by the conventional turning.

CuCrZr alloy, owing to its excellent comprehensive performance, has become an ideal material for manufacturing continuous casting mold copper plates. However, under harsh service conditions, mold copper plates encounter failures such as thermal fatigue cracks, creep deformation, surface wear/corrosion and cooling water erosion, etc. Existing surface repair and strengthening technologies still have certain limitations. Therefore, it is necessary to develop a new additive re-manufacturing technology for failed CuCrZr mold copper plates. Laser-assisted cold spray (LACS) is an emerging laser hybrid manufacturing technology that offers high deposition efficiency, minimal thermal damage to the substrate, and good interface bonding. It shows great potential for surface strengthening and additive manufacturing/re-manufacturing of metal components. In this study, LACS is employed to achieve additive re-manufacturing for failed CuCrZr substrates. The influence of different laser powers on the microstructure of the deposited layer is systematically discussed. Subsequent heat treatment of the re-manufactured layer is carried out considering actual service conditions, and the thermal conductivity and interface bonding strength of the re-manufactured layer are analyzed in depth. The results show that the introduction of laser irradiation significantly improves the bonding between the additive re-manufactured layer and the CuCrZr alloy substrate. Without laser irradiation assistance, obvious gaps exist at the interface between the deposited layer and the substrate. As the laser power increases, the gaps due to poor bonding at the interface are markedly reduced. At 1 500 W laser irradiation, the bonding interface between the deposited layer and the substrate is very tight. However, at 2 000 W laser irradiation, some pores appear at the bonding interface. The introduction of laser irradiation also helps to improve inter-particle bonding with the deposited layer. The porosity of the deposited layer without laser irradiation and with 1 000, 1 500 and 2 000 W laser irradiation are 6.27%, 3.52%, 0.43% and 0.56%, respectively. Wihout laser irradiation, the additive re-manufactured CuCrZr alloy layer contains a large number of larger-sized pores. As the laser power increases, the number of pores decreases and the deposited layer becomes denser. The average microhardness values of the deposited layer under 1 000, 1 500 and 2 000 W laser irradiation are 153.482, 167.714, 170.067 and 168.789 HV_0.2, respectively. Laser irradiation intensifies the plastic deformation of the deposited particles, inducing a work-hardening effect and thus higher hardness. XRD results show that the samples with laser irradiation and subsequent heat treatment maintain the same copper solid-solution phase as the sample without laser assistance, with no other imputity phase such as copper oxides detected. Post heat-treatment results reveal that the thermal conductivity of the 2 mm re-manufactured layer, the 1 mm re-manufacturing layer+1 mm substrate, the 2 mm substrate are 305.44, 315.92 and 334.2 W/(m·K), respectively. The thermal conductivity of the LACS-CuCrZr re-manufactured layer is close to that of the cast CuCrZr substrate, which is attributed to the dense microstructure of the LACS-CuCrZr re-manufactured layer. The interface bonding strength between the LACS-CuCrZr re-manufactured layer and the CuCrZr crystallizer substrate before and after heat treatment is 96.39 and 121.43 MPa, respectively. Due to the synchronous coupling laser heating, the plastic deformation at the material at the interface between the re-manufactured layer and the substrate is enhanced, resulting in a higher bonding strength. Moreover, the subsequent heat treatment further improves the interface bonding. The fracture morphology is characterized by pits formed by subsequent particle impact within the re-manufactured layer. The failure location lies within the coating, and the failure mode is typical cohesive failure. The bonding strength at the interface between the re-manufactured layer and the substrate is greater than that within the re-manufactured layer. The research results demonstrate that the additive re-manufactured CuCrZr alloy layer prepared at a laser power of 1 500 W exhibits excellent overall forming quality and outstanding comprehensive performance: porosity of 0.43%, microhardness of 170.067 HV_0.2, thermal conductivity of 334.2 W/(m·K), and interface bonding strength of 121.43 MPa. This work preliminarily verifies that LACS technology can serve as a new method for surface strengthening and additive re-manufacturing of crystallizer copper plates, providing a theoretical basis and technical support for its engineering application.

Numerical simulation of seal rubber contact friction is crucial in investigating seal failure mechanisms, and the accuracy of the seal contact surface modeling method is essential for reliable analysis. Traditional modeling approaches often suffer from high testing costs and insufficient precision in surface reconstruction, thereby limiting their effectiveness in practical applications. To address these challenges, this study proposes a novel sealing rubber contact surface modeling method that incorporates surface roughness characteristics. By integrating the 3D W-M fractal theory with the microconvex body theory, a mathematical model of the random height of the rough surface contour was established using surface roughness parameters as the initial input. This model included the fractal dimension and characteristic scale parameters to better characterize the complex surface topography of the sealing rubber. The generated rough surface contour was converted into a three-dimensional point cloud dataset, which was then imported into the UG software to form a coordinate point cloud matrix. A structured modeling approach was employed to sequentially construct points, surfaces, and solid bodies, resulting in a detailed 3D contact model of the rough surface of the sealing rubber. To evaluate the effectiveness of the proposed method, numerical simulations were conducted under applied loads ranging from 0 to 4 MPa for rubber sealing pairs with different surface roughness levels. The simulation results were compared with the experimental data to validate the reliability of the modeling approach. The analysis successfully determined the real contact area, contact state, and distribution characteristics of the contact stress, thereby providing valuable insights into the contact behavior of rough sealing surfaces. This study validates that the proposed method can effectively capture intricate roughness-induced contact variations, which are critical for understanding sealing performance and failure mechanisms. The proposed modeling technique relies solely on initial surface roughness parameters, eliminating the need for high-precision surface measurement instruments. By employing mathematical modeling and software-based surface reconstruction, this approach significantly reduces the measurement costs and complexity associated with specimen characterization. Moreover, the proposed method offers enhanced adaptability, allowing the analysis of diverse surface roughness conditions without requiring extensive experimental measurements. This study contributes to the field by developing an innovative contact surface modeling approach that integrates 3D W-M fractal and microconvex body theories, thereby enabling a more accurate representation of rough sealing surfaces. A structured modeling workflow was introduced to transform rough surface parameters into 3D point-cloud data, facilitating high-fidelity digital reconstruction. The proposed method was validated through numerical simulations and experimental comparisons, demonstrating its reliability in predicting real contact areas and contact state distributions under varying load conditions. By eliminating the need for high-cost surface-measurement equipment, this approach presents a cost-effective and practical alternative for engineering applications. This study presents an innovative surface modeling method for sealing rubber contact analysis that provides a more accurate and cost-efficient alternative to traditional modeling techniques. The ability to simulate and analyze rough surface contact characteristics without direct high-precision measurements enhances their applicability in both research and industrial settings. Future work will further refine the model by incorporating additional material properties and exploring its applicability to broader sealing performance analyses.

Since the nuclear leakage accident in Fukushima in 2011, accident-tolerant fuel (ATF) garnered significant attention. The development of coatings on existing Zr alloys to maintain the original design and structure of fuel assemblies has become a key research topic. Cr is widely used in Zr-alloy cladding coatings owing to its excellent corrosion and high-temperature steam oxidation resistance. Extreme high-speed laser cladding (EHLA) effectively addresses issues such as reduced corrosion resistance due to columnar coatings shown in other preparation techniques, inadequate adhesion between the coating and substrate, and excessive stress causing substrate deformation or cracking, thus demonstrating significant application prospects in surface modification. Therefore, investigating the preparation process, coating structure, corrosion resistance, and corrosion mechanism of EHLA Cr coatings is crucial for improving the performance of ATFs. In this study, Cr coatings are prepared on Zr alloy tubes using EHLA technology, and isothermal steam oxidation experiments are conducted at temperatures ranging from 900 to 1 300 ℃. The microstructural changes and oxidation kinetics are systematically analyzed. Isothermal steam oxidation experiments are performed in a tube furnace equipped with a steam generator. Before the experiments, Zr-alloy tubes and Cr-coated Zr alloy tube samples are cut into 1-cm-long semicircular segments and placed on alumina rods in crucibles to prevent oxidation on the inner surfaces. After evacuating the air from the tube furnace, argon gas at atmospheric pressure is introduced, followed by heating to 1 200 ℃ at a rate of 5 ℃/min. Steam is introduced through the steam generator for oxidation durations of 10, 30, 45, 60, 120, 180, and 240 min, followed by natural cooling to room temperature inside the furnace. Throughout the oxidation process, steam is introduced at a flow rate of 200 mL/min and a concentration of 50% via argon gas. An analytical balance (accuracy=0.01 mg) is used to measure the weight changes of the crucible and samples before and after oxidation. Cross-sectional characterization of the samples involve embedding in epoxy resin, grinding, polishing, and ultrasonic cleaning, followed by analysis using scanning electron microscopy and energy-dispersive spectroscopy. A ring compression test is performed using a 30 kN universal material testing machine. The hardness of the samples is measured using a Vickers hardness tester with a test load of 0.1 kg and a load time of 10 s. The samples are embedded in epoxy resin for fixation, thereby exposing the upper section for hardness testing. Research shows that Cr coatings deposited via EHLA exhibit a metallurgically dense structure, thus significantly improving the microhardness and ring compression performance of Zr-alloy pipes and decelerating the oxidation of the Zr matrix in high-temperature steam environments. At 1 200 ℃ in a steam oxidation environment, the laser-clad Cr coating provides at least 120 min of effective protection for the Zr-alloy substrate, with an oxidation weight gain of only 43.5% compared with that of uncoated Zr alloy samples. After 120 min of oxidation, accelerated coating failure occurred owing to increased oxidation and elemental interdiffusion, thus resulting in cracks and pores on the surface and internally; consequently, protection for the Zr alloy is nullified after 240 min. Meanwhile, the clad samples exhibit good stability within the temperature range of 900-1 300 ℃, although their oxidation resistance decrease with increasing temperature. The experimental analysis and kinetics cumulatively show that the power-law oxidation model can accurately predict the oxidation behavior of Cr coatings in high-temperature steam environments to some extent, thus providing an important reference for assessing the oxidation extent of other coatings. Therefore, high-speed laser-clad Cr coatings offer effective protection for ATF cladding materials under extreme conditions. By analyzing the oxidation and failure behaviors of laser-cladding Cr coatings in high-temperature steam environments, the corrosion process and failure mechanism in extreme environments can be investigated comprehensively, thus providing new ideas for solving the oxidation problem of Zr alloy cladding in extreme environments.

High-grade ceramics and their composite materials, optical glass, and other brittle materials exhibit excellent properties such as high hardness, low density, high heat resistance, wear resistance, and high chemical stability. They are widely used in aerospace, rail transit, medical devices, national defense, and other industries. Particularly in the aerospace sector, thermal structural components and hot end components must withstand extreme temperatures, mechanical loads, and oxidizing environments. Hard and brittle material components often require very high surface integrity and dimensional accuracy, and efficient precision grinding is an important step. In addition, the surface integrity of high-temperature components made of hard and brittle materials directly affects their properties and fatigue performance. The traditional grinding process still has limitations such as surface damage, tool wear, and low machining efficiency. Therefore, the realization of efficient and precise machining of such materials has become a key problem that must be urgently addressed in the advanced manufacturing field. As a state-of-the-art technology in the precision machining field, ultrasonic vibration-assisted grinding (UVAG) provides a new method for the efficient and low-damage machining of high-temperature structural parts made of hard and brittle materials through the combined action of high-frequency vibration and grinding. In particular, the unique advantages of UVAG in handling flat, deep hole, thin-walled, and complex hard-brittle material surfaces make it the preferred solution for solving these bottlenecks. A systematic study of material removal mechanisms and surface formation is required. However, existing research has mostly focused on macroscopic ultrasonic machining, lacking of targeted analysis of the ductile-brittle transition mechanism of hard-brittle materials. The relationship between the mechanical properties of abrasive materials and the material removal mechanism has been extensively studied. In this study, the brittle transition mechanism of hard-brittle materials was revealed, and the brittle fracture and ductile deformation removal behaviors of different hard-brittle materials were analyzed. The nucleation and propagation rules of radial and transverse cracks were studied, and ductile removal models characterized by different parameters of different hard-brittle materials were studied. The mechanisms of grinding removal and damage to hard and brittle fiber composites by UVAG were analyzed. Then, by analyzing the mechanical behavior and response characteristics of UVAG hard-brittle materials, a grinding force analysis model of different hard and brittle materials was studied under different UVAG vibration modes, and an error comparison was conducted. The relationships between the grinding and ultrasonic vibration parameters and the grinding mechanics and surface integrity were elucidated. Furthermore, the generation mechanism of hard and brittle material surfaces under the influence of dynamic and nonlinear characteristics of high-frequency and low-amplitude ultrasonic vibration is explained, and the positive influence of ultrasonic vibration on grinding wheel wear was analyzed. Next, a prediction model for the surface evaluation parameters of UVAG hard-brittle materials was studied. Multi-parameter control strategies for surface integrity, such as grinding damage, subsurface damage, surface roughness, and residual stress, were studied. The performance advantages and multi-parameter optimization of UVAG hard-brittle materials were analyzed. The influences of different grinding and ultrasonic parameters on the parameters of ultrasonic-assisted end and peripheral grinding are summarized. The reduction effects of grinding force and surface integrity under different ultrasonic amplitudes were compared. Finally, the existing technical bottlenecks of hard-brittle material grinding were analyzed, including the dynamic fracture behavior of hard-brittle materials under ultrasonic vibration and the formation mechanism of the surface / SSD layer, and there is no intelligent parameter co-optimization method based on material characteristics and grinding objectives. In addition, the development directions of theory, technology, equipment, and applications are expected to provide technical support and theoretical guidance for industry and academia.

The main bearings of large-scale wind turbines are continuously exposed to extreme working conditions for a long time. Under the long-term cyclic contact stress, the rolling elements and the bearing rings of the main shaft bearings will incur fatigue damage. This situation prompts the bearing raceways of the wind turbine main shafts to possess extremely high load-carrying capacity, fatigue resistance, and reliability, so as to deal with the complex loads during long-term operation. With the development of the laser technology field, the laser solid-state phase transformation technology has high action precision, a small heat-affected zone, and the capability to conduct solid-state phase transformation on the selected areas. It has become a suitable and effective method for improving the mechanical properties of wind turbine bearings. However, its influence on the subsequent service damage of the materials is still not clear. In order to explore the influence of laser solid-state phase transformation on the surface properties of the 42CrMo bearing raceway material and the initiation and propagation mechanism of cracks after phase transformation, the surface of 42CrMo steel is subjected to single laser solid-state phase transformation and laser-induction hybrid solid-state phase transformation treatments. The variation laws of the microstructure and hardness of the materials under different treatment processes are analyzed. Through the MJP-30A rolling wear and contact fatigue testing machine, the influence of different phase transformation methods on the rolling wear and contact fatigue properties of 42CrMo steel is compared and analyzed. The results show that during the single laser solid-state phase transformation process, due to the multi-pass laser overlapping, a hardened zone composed of martensite and a softened zone composed of tempered martensite are formed. The average surface hardness of the softened zone is 405 HV_0.2, and the average surface hardness of the hardened zone is 562 HV_0.2, which is 87.96% higher than that of the substrate. After the laser-induction hybrid solid-state phase transformation, the microstructure is entirely composed of martensite, and the average hardness is 724 HV_0.2, which is 28.83% higher than that of the hardened zone in the single laser solid-state phase transformation. After the rolling contact wear under dry conditions, compared with the untreated specimen, the wear amounts of the specimen with single laser solid-state phase transformation and the specimen with laser-induction hybrid solid-state phase transformation are decreased by 93.20% and 96.14%, respectively. The higher the hardness of the material is, the thinner the thickness of the plastic deformation layer is. The thickness of the plastic deformation layer of the untreated specimen gradually decreases with the increase of the number of cycles, while the thickness of the plastic deformation layer of the laser solid-state phase transformation specimen shows no obvious change with the increase of the number of cycles. During the rolling contact process, when the plastic deformation exceeds the plastic strain limit, cracks begin to initiate. For the untreated specimen, the cracks propagate rapidly through the grains. After the cracks break through the plastic deformation layer, they bend and then continue to propagate in an almost horizontal direction. The surface cracks intersect, resulting in material spalling. At the same time, vertical cracks will be generated above the oblique cracks, which will also lead to material fracture and spalling. For the specimen with single laser solid-state phase transformation, none of the cracks break through the plastic deformation layer. In the softened zone, there are mostly delamination cracks, and the interlayer materials are prone to fracture under the action of the cyclic normal force. For the specimen with laser-induction hybrid solid-state phase transformation, after the cracks propagate with a trend parallel to the surface, they are fractured under the shear stress, forming spalling pits. After the laser solid-state phase transformation treatment, the wear resistance and fatigue resistance of 42CrMo steel are significantly improved. Among them, the improvement of the wear resistance and fatigue resistance of the laser-induction hybrid solid-state phase transformation is the most remarkable.

Gears constitute the core components of helicopter reducers, and the failure of heavy-load transmission gears directly impacts the reliable operation of the reducer, potentially endangering the service safety of the helicopter. Enhancing the service performance and reliable working margin of gears through surface post-treatment technologies holds significant military and economic value. Laser shock peening, as an advanced surface strengthening technique, aims to achieve efficient surface modification of metallic materials. However, its application to geometrically complex parts presents technical challenges. Therefore, an attempt is made to modify the surface of gears using laser shock peening without coatings. To verify the efficacy of laser shock peening without coatings in improving the properties of gear steel, strengthening experiments are conducted with varying process parameters. The experiment innovatively employs a smaller spot size and lower energy level for processing. Specimens of specific material grades undergo grinding, vacuum carburizing, and heat treatment to simulate the transmission gears of a reducer, providing a process reference for real gear components. AISI 9310 steel, a typical martensitic steel, is selected for study. The sample exhibits a complete carburized layer of approximately 420 μm, with a stable hardness of 625 HV within this range. Beyond 1 000 μm, where the matrix is entirely outside the carburizing zone, the hardness stabilizes at 430 HV. The laser beam interacts directly with the specimen in an atmospheric environment. Given the unique structure of gear parts, a water-optical coaxial strengthening method is adopted. During the optimization of the laser process, laser energy is first optimized, followed by the number of laser shocks. The effects of laser parameters on mechanical properties and surface morphology are systematically analyzed. The samples are characterized using an optical microscope, microhardness tester, residual stress meter, roughness meter, and atomic force microscope. The results indicate that laser shock peening without coatings introduces a maximum work-hardened layer of 530 μm and a residual compressive stress layer of 450 μm in the depth direction of the sample. The substantial improvement in subsurface mechanical properties is attributed to the plastic deformation induced by the plasma shock wave in the gradient direction. After strengthening, the maximum hardness reaches 689.9 HV, and the residual compressive stress increases to 738.9 MPa. The direct irradiation of the laser beam on the sample surface leads to heat accumulation, causing a rapid increase in surface roughness to a maximum of 1.509 μm. This results in the formation of a periodic micro-convex structure with a regular arrangement. As laser energy and the number of shocks increase, this structure gradually evolves into a regular rectangular pattern, exhibiting self-lubrication properties. An effective work-hardening layer is formed along the depth direction of the specimen after strengthening. An increase in laser energy or frequency significantly enhances the work-hardening effect of laser shock peening without coatings. Additionally, a high-amplitude residual compressive stress is introduced into the specimen along the depth direction, forming a residual compressive stress layer with the same thickness as the hardened layer. The results of process optimization reveal that a surface treated with 120 mJ per strengthening cycle, applied twice, forms a periodic rectangular microstructure pattern, resulting in the most significant improvement in comprehensive mechanical properties. The influence of laser shock peening without coatings process parameters on the properties of AISI 9310 steel is studied, and the process parameters are further optimized. The effectiveness of laser shock peening without coatings in improving the mechanical properties of gear steel materials is verified, providing data accumulation and technical support for the subsequent enhancement of friction performance, rolling contact fatigue performance, and bending fatigue performance of gears.

During the operation of the plant, the corner area of the spent fuel pool is prone to corrosion, which causes the risk of leakage. Locally dry underwater laser welding provides an accurate solution to this in-service maintenance problem. To meet the needs of repairing the corner crack defects of the spent fuel tank, we have built a test platform that supports local dry underwater laser keracy test at atmospheric pressure and high pressure. We selected S32101 dual-phase stainless steel as the test material, and carried out the multi-channel process test of local dry underwater laser wire filling angle welding in air, underwater and simulated water depth of 20 m. The macroscopic cross-sectional morphology and microstructural characteristics of fillet welds were examined and compared across three distinct environments. The findings indicated that the fillet weld sections were free from defects such as porosity and inclusions, with a clear delineation of the fusion line between welds. The welds exhibited robust bonding with each other and with the base metal. Notably, the fillet welds produced in a high-pressure underwater environment were found to be thicker than those in a normal-pressure environment, while the weld leg dimensions were observed to be smaller. This was attributed to the slower cooling rate of the molten pool in an air environment, which allowed austenite sufficient time to grow, resulting in the finest grain size observed in the high-pressure underwater environment. Additionally, the degree of grain size nonuniformity was greater in the underwater environment compared to the air environment, where the largest grain size was recorded. Electron backscatter diffraction (EBSD) was employed to examine weld samples in both underwater and high-pressure underwater conditions using the Thermo Scientific Apreo 2C+EDAX Velocity Super. The analysis determined the composition, orientation, texture, and boundary characteristics of ferrite and austenite. The findings indicated that the austenite content was 45.3% in the underwater environment and 38.3% in the high-pressure underwater environment. This disparity is attributed to the fact that the phase equilibrium composition of ferrite relative to austenite is higher than that in the specified composition equilibrium state, a result of the rapid cooling of the weld metal. As the welding environment transitions from underwater to high-pressure underwater conditions, the grains exhibit a progressively more pronounced orientation. The disparity in grain size non-uniformity is more pronounced in high-pressure underwater settings compared to standard underwater conditions, resulting in a more pronounced preferred orientation. This phenomenon can be attributed to the enhanced cooling capacity of the water at depth, which alters the grain structure, increases the instability of the welding process, affects the distribution of the heat source, and consequently leads to a greater nonuniformity in grain size. The average Kam value for underwater laser welding is 0.58, while in a high-pressure underwater environment, it increases to 0.64. The austenite grain boundary exhibits a bimodal distribution characterized by low-angle boundaries (LABs) at 15 degrees and high-angle boundaries (HABs) at 50 degrees. Furthermore, the bimodal distribution trend of the austenite grain boundary becomes more pronounced in high-pressure underwater conditions.The multi-layer and multi pass fillet welds in three environments have good intergranular corrosion resistance. Through the test and analysis of open circuit potential, impedance spectrum and polarization curve, it is found that the corrosion resistance of fillet weld in different environments is air environment fillet weld>high pressure underwater environment fillet weld>underwater environment fillet weld>base metal. In conclusion, the simulation of multi-layer and multi-channel fillet welds within 20 m water depth can meet the repair needs of nuclear power projects, and the research results have laid a good foundation for the crack repair at the corner of the spent fuel pool in nuclear power plants.

With the rapid advancement of industries such as aerospace, shipbuilding, high-speed rail, petroleum, and chemical engineering in China, the demand for high-strength metallic materials has increased significantly. However, when these materials are exposed to hydrogen-containing environments, they are susceptible to a unique form of fracture failure known as hydrogen embrittlement. The application of hydrogen barrier coatings on metal surfaces offers a promising approach to preventing or delaying hydrogen ingress, thereby mitigating embrittlement and enhancing material durability. As a result, hydrogen-induced degradation remains a critical challenge for protective coatings used in hydrogen-rich environments, particularly in the petroleum and chemical sectors. In this context, two-dimensional (2D) nanomaterials have attracted considerable scientific and engineering interest due to their excellent structural and physicochemical properties. Their high surface-area-to-thickness ratios differ markedly from those of conventional 3D bulk materials. MXenes, a class of emerging 2D nanomaterials, have attracted widespread attention due to their tunable mechanical and electrical properties, excellent hydrophilicity, high charge mobility, outstanding flexibility, and good compatibility with various matrices. These materials are typically synthesized by selectively etching the “A” layers from bulk MAX phases (ternary carbides and nitrides), followed by exfoliation, using etchants such as LiF-HCl, HF, and HF salts. As either standalone coatings or nano-fillers, MXenes have garnered increasing interest in the field of metal surface protection. Numerous studies have demonstrated that MXenes can effectively inhibit the penetration of corrosive species owing to their well-defined two-dimensional structure and strong physical barrier effect. Moreover, these characteristics endow the MXene-based material with excellent protective performance. Nevertheless, theoretical investigations into the ability of MXenes to inhibit H diffusion, particularly with consideration of surface functionalization, remain limited. Therefore, elucidating the interaction mechanisms of H on MXene surfaces at the micro-electronic scale is of significant importance. In this study, the adsorption and diffusion behaviors of H on pristine Ti₃C₂ and functionalized Ti₃C₂Ti₂ (-F/-O/-OH) surfaces were systematically investigated using first-principles calculations. By analyzing adsorption configurations, adsorption energies, differential charge densities, electronic density of states, and diffusion energy barriers, the mechanisms governing H diffusion inhibition were clarified from both thermodynamic and kinetic perspectives. The results indicate that the adsorption energies of H on functionalized Ti₃C₂F₂, Ti₃C₂O₂, and Ti₃C₂O₂H₂ are significantly higher than those on pristine Ti₃C₂. The adsorption energies of H on vacancy V-Ti₃C₂F₂, V-Ti₃C₂O₂, and V-Ti₃C₂O₂H₂ follow a similar trend to that observed for V-Ti₃C₂, with the highest adsorption energy occurring on the F-functionalized Ti₃C₂F₂ surface. The diffusion energy barrier of an H atom on the pristine Ti₃C₂ surface is slightly lower than that on the vacancy-containing V-Ti₃C₂ surface. Furthermore, the diffusion energy barriers of H on V-Ti₃C₂O₂ and V-Ti₃C₂O₂H₂ surfaces are significantly higher than those on Ti₃C₂O₂ and Ti₃C₂O₂H₂ surfaces without vacancies. However, the diffusion energy barriers of H atoms on both Ti₃C₂F₂ and V-Ti₃C₂F₂ are negative, indicating their relatively poor effectiveness in inhibiting H diffusion. The diffusion energy barriers of H atoms on Ti₃C₂O₂ and Ti₃C₂O₂H₂ surfaces are significantly increased compared to those on pristine Ti₃C₂, with the diffusion energy barrier reaching a relatively high value on the Ti₃C₂O₂ surface. In particular, the diffusion energy barrier of H on the V-Ti₃C₂O₂ surface attains a maximum value in the presence of vacancies, which is much higher than that on the Ti₃C₂O₂ surface without vacancies, demonstrating an effective blocking effect on H diffusion. These findings provide an important theoretical basis for the design of MXene-based protective materials in hydrogen-containing environments.

：To address the insufficient wear resistance and limited service life of magnetic particle clutches and braking devices utilizing pure iron substrates—characterized by excellent magnetic properties but low hardness and poor durability—this study proposes a surface engineering strategy involving plasma ion nitriding with hot filament enhancement. This approach aims to fabricate a wear-resistant nitrided layer with preserved magnetic permeability, thereby extending operational longevity while maintaining cost-effectiveness. Compared to conventional gas nitriding, plasma ion nitriding offers superior advantages, including enhanced energy efficiency, precise control over the nitrided layer structure, and broader applicability to challenging materials. The introduction of tungsten filaments within the vacuum chamber significantly enhanced gas ionization, thereby accelerating the nitriding kinetics and improving the process efficiency. Under optimized conditions (520 ℃, 0.4 Pa), systematic variations in the atmosphere and thermal processes were employed to investigate the catalytic role of hydrogen and the effects of staged thermal alloying (insulation). The phase composition, cross-sectional morphology, layer depth, and tribological properties of the nitrided layers were characterized by X-ray diffraction (X’Pert Powder), scanning electron microscopy (ΣIGMA HD), micro-Vickers hardness testing (Q10M), tribometry (MS-T3001), and step profiler (Alpha-step D-100). Results indicate that a pure nitrogen atmosphere produced a 500 μm-thick nitrided layer comprising ε-Fe₃N (29%) and γ'-Fe₄N (71%) phases, with a curved compound-diffusion layer interface due to low nitrogen diffusivity (13.88 μm²/s) and preferential short-circuit diffusion along grain boundaries. Within the diffusion layer, nitrogen atoms dissolved into the octahedral interstices of the ferrite lattice. The nitrogen atoms exceeded the solubility limit of the ferrite precipitates as nitrides. Two distinct precipitation morphologies were observed: relatively long needle-like nitrides preferentially precipitated at the grain boundaries, whereas comparatively shorter rod-like nitrides were dispersed intragranularly. This intragranular precipitation pattern adhered to the Baker-Nutting orientation. In contrast, the introduction of hydrogen and the two-stage thermal alloying markedly altered the phase distribution and diffusion dynamics. The modified process yielded a 1 000 μm-thick nitrided layer with a refined phase ratio (6% ε-Fe₃N vs. 94% γ'-Fe₄N) and enhanced nitrogen diffusivity (55.55 μm²/s). Hydrogen mediation promotes homogeneous lattice diffusion, resulting in a planarized compound-diffusion interface. Notably, a 600 μm-wide hardness plateau (100-700 μm depth) emerged due to nitrogen redistribution during alloying stages. This plateau arose from the decomposition of nitrogen-rich phases under an interrupted nitrogen supply, followed by inward nitrogen migration driven by concentration gradients and solid-solution strengthening. The plateau with a relatively slow change in the hardness value provides good support for the hard and brittle compound layer-soft matrix. Meanwhile, under the optimized processes, the diffusion rate of nitrogen increased significantly, and the hardness of the nitriding diffusion layer was enhanced by solid-solution strengthening. The synergistic effects of these two factors weakened the “eggshell effect.” The synergistic effects of hydrogen and staged alloying significantly improved the mechanical and tribological performance. Wear rate decreased by 15-fold (from 2×10^-4 to 1.3×10^-5 mm³·N^-1·m^-1), while the friction coefficient dropped by 42.9% (0.42→0.24). The width and depth of the friction and wear marks decreased significantly, and the microstructural analysis revealed a transition in wear mechanisms from severe adhesive/oxidative wear to mild abrasive wear, which was attributed to the support of the hardened subsurface platform for the brittle compound layer. Crucially, the magnetic properties of the pure iron substrate remain uncompromised; for example, it exhibits good saturation magnetization and extremely low coercivity. This work demonstrates that hydrogen-enhanced plasma nitriding coupled with staged thermal alloying enables the fabrication of ultrathick, mechanically graded nitrided layers with balanced strength-toughness properties. These findings provide novel insights for industrial applications of plasma nitriding, offering a viable pathway to enhance the surface durability of magnetic components without sacrificing their intrinsic functional performance. The proposed methodology has a significant potential for advancing precision manufacturing and automated systems that require highly reliable and extended service intervals.

Electrical connectors are widely used in the aerospace industry, rail transit, and new energy vehicles. As typical current-carrying frictional pairs, electrical connectors are key components that determine equipment power and signal transmission. With the continuous advancement of electrification, the reliability and performance requirements for electrical connectors have become more stringent. Unlike traditional mechanical wear, the friction and wear of electrical contacts under current-carrying conditions are influenced by force-thermal-electrical coupling effects, leading to more complex failure modes and damage types. Consequently, the failure mechanisms of electrical connector contacts have attracted significant attention in both academic and industrial fields. Ag is one of the most commonly used coating materials for electrical contact surfaces. To investigate the damage mechanisms of Ag-coated electrical contacts, a sliding current-carrying wear test was conducted using ball-disk frictional pairs. Single-point contact was used to simulate the friction and wear of a single-contact finger during the insertion process. During the experiment, the changes in current-carrying properties and the evolution of material damage mechanisms were examined under different current densities. The results showed that the average friction coefficient in the steady state increased with an increase in current density in the contact area. At high current densities (21.4 and 35.7 A/mm²), the friction coefficient suddenly changed after a period of smooth operation. Furthermore, as the current density increased, the timing of this abrupt change occurred earlier: at 21.4 A/mm², the average friction coefficient during stabilization was approximately 1.01, followed by a sudden drop to about 0.69 at 1 050 s. At 35.7 A/mm², the friction coefficient experienced an abrupt change at 700 s, decreasing from 1.1 to 0.72 within 10 s. The oxygen contents in the wear zones of the ball and disk under different operating conditions were compared. Due to passivation from Ni oxidation, surfaces with high Ni content exhibited no significant oxidation (disk samples at current densities below 7.2 A/mm²). The degree of oxidation in the wear zone increased after the appearance of Cu on the surface. At 35.7 A/mm², the oxidation level of the disk sample was higher than that of the ball sample. Because the ball was ground repeatedly along the same circular path on the disk surface, its exposure to the external atmosphere was limited during grinding friction, resulting in relatively lower oxidation. The current-carrying wear mechanism of the composite coating involved adhesive wear accompanied by abrasive and oxidative wear. Arc ablation was not observed in this study. The temperature increase at the contact interface of the friction pair resulted from the combined effects of frictional heat and Joule heat, with frictional heating predominating at low current densities. When the current density exceeded 7.2 A/mm², Joule heat played a dominant role in the temperature rise, which increased rapidly with increasing current density. Temperature increase is the primary mechanism by which current promotes adhesive wear; it softens the contact material and alters the properties of the contact interface. This research not only provides a simple and effective approach for analyzing the current-carrying performance and wear mechanisms of silver-plated electrical contacts under varying current densities but also offers a theoretical foundation for the reliable design and damage protection of silver-plated electrical connector contacts.

The solar sail drive plays a pivotal role in the sustainable energy supply of satellites. In the long-term transmission process of current and signals, approximately 20% of solar sail drive device failures are attributed to friction wear and lubrication failure, resulting from conductive slip ring short circuits and stuck conditions. It is noteworthy that the majority of conductive slip ring materials currently employed are gold alloys. However, the use of gold alloys in these devices can lead to an increase in resistivity, thereby reducing the overall effectiveness of the system. To enhance the friction performance of the gold-based coating, it is imperative to minimize the increase in resistivity of the coating. To this end, the present study employed DC magnetron sputtering to prepare gold-based coatings on CuCrZr alloys and Si wafers, with target sputtering powers of 0, 30, 50, and 100 W, respectively. The transition layer comprised a 150 nm-thick Ni layer, which was subjected to annealing treatments at 250 ℃ for 5 and 20 h. The coatings were also subjected to a series of characterization and experimentation to investigate the effects of co-doping Ni and Cr and performing vacuum annealing treatment on the structure and comprehensive properties of the coatings. The properties investigated included resistivity, residual stress, nano-hardness, and friction and wear properties. The results demonstrate that the atomic percentages of Ni and Cr elements in the coatings increase with the increase of sputtering power of Ni and Cr targets, and the vacuum annealing treatment does not produce large changes in the atomic percentages of Ni and Cr elements.The Au, Ni, and Cr elements in the coatings show a homogeneous distribution, and the vacuum annealing treatment does not have an effect on the homogeneous distribution of the Au, Ni, and Cr elements. The coatings exhibit optimal orientation, characterized by the presence of (111) and (220) diffraction peaks. The incorporation of Ni and Cr into the coating material results in a diminution of the intensity of the (111) diffraction peak. The effect of annealing treatment on (111) diffraction peak intensity is complex. The modification of the coating grain size by Ni, Cr doping and annealing treatment is multidimensional. Increasing the Ni, Cr target power and annealing both lead to an increase in resistivity, a decrease in residual stress, and even a change in type and increase in nanohardness of the coating. The lowest coefficient of friction for pure gold coatings is due to the high plasticity of gold, while the highest wear rate is due to the low hardness of gold. Doping with Ni, Cr leads to an increase in the coefficient of friction and a decrease in the wear rate of the coating. The fluctuation of the friction coefficient of the coating flattens out as the Ni, Cr target power increases. Vacuum annealing treatment gradually improves the fluctuation of the friction coefficient of the coating. After the vacuum annealing treatment, the friction coefficient increases with the extension of the annealing time, and the wear rate increases and then decreases with the extension of the annealing time, which is related to the change of the overall properties of the coatings after the annealing process.There is an adhesion phenomenon on the friction surface of the coatings with the Ni, Cr target power of 0 W, which indicates that the wear of the coatings is mainly based on adhesive wear and plastic deformation. With the increase of Ni, Cr target power, fuzzy furrows appeared on the friction surface of the coating, indicating that the wear of the coating was dominated by abrasive wear and fatigue wear. The co-doping of Ni, Cr and the solid solution strengthening and fine crystallization due to the annealing treatment would increase the nanohardness of the coatings and thus improve the wear resistance. However, there is no significant inhibitory effect on the resistivity increase.

Metal-air batteries have attracted extensive attention due to their exceptional energy density, large capacity, and low cost. Among them, aluminum-air batteries, as a new type of energy storage equipment with great potential, have important application prospects in future energy storage fields. However, aluminum-air batteries face a major obstacle in practical applications: the hydrogen evolution reaction of the anode leads to low anode utilization, which considerably affects the performance and life of the battery. To solve this problem, this study aims to inhibit hydrogen evolution by preparing a metal-organic framework (Mn-MOFs) coating on the surface of an aluminum alloy anode to improve the electrochemical performance and anode utilization of aluminum-air batteries. In this study, a Mn-MOF coating was prepared on the anode surface of an aluminum alloy via one-step electrodeposition. First, the microstructures of the Mn-MOF coatings were analyzed in detail using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Subsequently, the corrosion resistance of the coating and its effect on the anode utilization were evaluated using electrochemical and hydrogen evolution corrosion tests. The effects of different deposition times (10, 20, and 30 min) on the electrochemical properties of Mn-MOF coatings were studied. To further understand the anti-corrosion mechanism of the Mn-MOF coating, the study combined quantum mechanical calculations to simulate the interaction between the coating and the aluminum anode and its inhibitory effect on the hydrogen evolution reaction. The experimental results showed that when the deposition time of the Mn-MOF coating was 20 min, the aluminum-air battery exhibited the best electrochemical performance. SEM and EDS analyses showed that the coating layer had a dense structure and uniformly covered the aluminum alloy surface, which effectively prevented the OH^- in the electrolyte from directly contacting the aluminum alloydirectly. FT-IR and XPS analyses confirmed the successful preparation of the Mn-MOF coating layer and revealed its chemical composition and valence bond states. Electrochemical tests showed that the Mn-MOF coating significantly reduced the hydrogen evolution rate of the anode, thereby improving its utilization rate. A hydrogen evolution corrosion test showed that the coating significantly extended the lifetime of the Al alloy anode. The quantum mechanical calculation results show that, owing to its unique chemical structure, when the Mn-MOF membrane is consumed, the (-COO-) in the aromatic acid can react with Al³⁺ in solution to form the RCOO-Al complex, which is deposited on the electrode surface, inhibiting the diffusion of intermediate products into the solution. This effectively inhibits the hydrogen evolution reaction. This can significantly improve the electrochemical performance and anode utilization of Al-air batteries. In addition, this study applied a Mn-MOF coating layer to the anode protection of aluminum-air batteries, and through systematic experiments and theoretical analysis, through a series of experiments and simulations, the anti-corrosion mechanism of the Mn-MOF coating layer was discussed, which opens up a new method for the surface treatment of metal-air batteries and provides an important theoretical basis and technical support for the performance optimization of metal-air batteries in the future.