Macroscopic solid superlubricity (with a friction factor on the order of 0.001) in diamond-like carbon (DLC) films has attracted widespread attention in the academic community in recent years due to its significant potential in the domain of solid lubrication under extreme working conditions, such as vacuum, high contact pressures, and wide temperature ranges. However, the deposition methods and bonding structures of DLC films are diverse, and specific intrinsic compositions and structures, as well as external working conditions, are required to achieve macroscopic superlubricity in DLC films. Thus, this review discusses current research progress on the structural regulation of DLC films, diverse superlubricity behaviors in DLC films, key influencing factors, and their corresponding mechanisms. First, the current structural classification, deposition methods, and recent research on the bonding structure regulation principles of DLC films for solid superlubricity were summarized. An effective strategy for synthesizing DLC films with superior solid superlubricity is to adjust the composition and energy of deposition ions to balance the surface chemisorption and subsurface implantation growth modes, leading to an optimized combination of mechanical stiffness and hydrogen content of DLC films. Subsequently, the research trajectory on superlubricity in DLC films was reviewed, and the latest developments categorized by mechanisms were introduced. The combinations of DLC and environmental media available for superlubricity are diverse, and include hydrogenated amorphous carbon (a-C:H) in dry inert atmospheres, doped a-C:H in humid air or water-based liquids, hydrogen-free DLC in oil-based liquids, and DLC films in nanomaterial-containing environments. Furthermore, the influencing mechanisms of the internal elemental composition and bonding structure of DLC films, as well as external working conditions such as the environment, contact pressure, and temperature on the superlubricity behavior of DLC are discussed in detail. Sufficient hydrogen content is necessary for DLC films to achieve superlubricity in dry inert atmospheres, such as N₂, Ar, and vacuum. The self-lubrication properties of DLC films can be significantly affected by O₂ and H₂O molecules in humid air, due to intensified interfacial chemical bonding, disordered water adsorption layers, enhanced hydrogen bonding forces, and van der Waals forces caused by tribo-chemically generated highly polar groups. Elemental doping with Si, S, and Ti can effectively suppress the moisture sensitivity of DLC films via their participation in the structural evolution of sliding interfaces. Sufficiently high contact pressure is also necessary for solid superlubricity in DLC films, which is mainly due to the self-lubrication effect of contact-pressure-triggered locally short-range-ordered layered-like sp² nanoclustering structures. Overly high contact pressure deteriorates the superlubricity state of DLC films through hydrogen detachment and microstructural destruction of the counterpart surfaces. Ultralow temperature (<-100 ℃) can increase the friction factor of DLC films due to the suppression of thermal activation and structural evolution of sliding interfaces. On the contrary, high temperature (>300 ℃) facilitates the failure of a-C:H films due to excessively promoted hydrogen detachment, graphitization, and oxidation in air. Additionally, the mechanism behind the solid superlubricity of DLC is discussed from the perspective of interfacial bonding structural evolution. The tribo-generated transfer films on smooth-stiff surfaces, hydrogen passivation of surface dangling bonds, and generation of short-range ordered graphite-like nanostructures are key factors for the establishment of superlubricity in DLC films, which simultaneously suppress the three main contributors of macroscopic friction force: interfacial abrasion, shearing, and adhesion effect. Finally, the unresolved issues and related research trends in the underlying science and engineering applications of DLC are summarized. The connection of deposition parameters with growth theories, the nanostructure of superlubricious sliding surfaces and their evolutionary pathway, the environment and working condition sensitivity, and the influencing mechanisms of multi-element, multilayer, micro-nano textured, and media-synergistic lubrication strategies require further research. These findings can provide technical support for the design and application of superlubricious DLC films for dry-sliding friction pairs under extreme engineering conditions.

In the current era of industrial manufacturing and materials science, continuously enhancing material properties to meet the growing application challenges is an ongoing task. Metal materials play a key role in many industries because of their excellent mechanical properties and wide range of applications. Nevertheless, these metals are often subjected to wear, corrosion, and fatigue damage during practical use, which severely reduces their service life and reliability. Therefore, studying effective surface modification technologies that can improve the surface integrity and properties of metals has become a core issue in materials science research. Ultrasonic surface rolling processing (USRP) is an advanced material surface modification technology that combines ultrasonic energy and high-frequency mechanical vibrations to nano-strengthen the metal surface. This technology can cause plastic deformation on the surface of the material and significantly improve its surface integrity and mechanical properties. USRP can generate residual compressive stress on the surface of a material, effectively preventing the formation and expansion of cracks and reducing the permeability of the corrosive medium. In addition, this technology can form a nanostructured layer with a gradient grain size and orientation, thereby significantly enhancing the surface hardness and wear resistance of the material. This review summarizes the research progress in USRP in the fields of steel, aluminum alloy, titanium alloy, magnesium alloy, nickel alloy, and high-entropy alloy. It is demonstrated that these materials have achieved remarkable results in surface nano-strengthening and microstructural and performance improvement following USRP treatment. USRP technology can not only refine the grain size, reduce the surface roughness, and improve the surface hardness, but also convert the residual tensile stress into residual compressive stress to obtain a deeper nano-gradient hardened layer and residual compressive stress-affected area. This compensates for the low production efficiency of traditional mechanical processing methods as well as the mismatch between the working environment and performance requirements of high-performance materials. Finally, future application prospects and development directions of USRP are discussed. It is expected that focus will be placed on the refinement of theoretical models and the diversification of working methods. This research will further explore the theory of contact mechanics and surface integrity to develop a prediction model that can optimize the process parameters. In addition, USRP technology will be adapted to deal with complex parts and improve the efficiency and performance through multi-field coupling and process integration. The expansion of the application range will include composite materials and high-tech fields, including deep-sea exploration and aerospace satellites.

Inspired by Nepenthes pitcher plants, slippery liquid-infused porous surfaces (SLIPS) were first created in 2011 to offer a novel approach to surface engineering. Unlike conventional superhydrophobic surfaces (SHS), which rely on air lubrication, SLIPS utilize liquid lubrication with superior durability and pressure stability. With such advances, SLIPS possess outstanding liquid and ice repellency, self-healing, and enhanced optical transparency, which can be implemented in a wide range of energy applications, such as industrial anti-icing, anti-fouling, anti-frosting, and droplet-based power generation. Because most industrial application scenarios for SLIPS frequently encounter impacts of droplets, a mechanistic understanding of the dynamic interactions between SLIPS and impacting droplets is essential for the effective use of SLIPS under specific application conditions. This review systematically examines droplet impacting dynamics on SLIPS. In section 1, we introduce the thermodynamic conditions required to form effective SLIPS and their fabrication methods. There are two major criteria to achieve stable SLIPS: 1. lubricant spreading on the substrate, characterized by the spreading parameter (S) and 2. stabilization by van der Waals forces, characterized by the disjoining pressure or corresponding Hamaker constant (A). The fabrication of SLIPS involves structural treatments on substrates that are followed by chemical functionalization and the final lubrication selection. Based on the substrate structure, SLIPS can be categorized into 1D-SLIPS, 2D-SLIPS, and 3D-SLIPS based on the structural hierarchies varying from one-dimensional mono-molecule layers to two-dimensional micro- / nano-surface structures to three-dimensional crosslinked polymer matrices, respectively. In section 2, we summarize the dynamic behaviors of droplet impacts on SLIPS, including deposition, complete rebound, partial rebound, jet, and splash behaviors under conditions with different Weber numbers or other related dimensionless numbers. As the Weber number increases, the dynamic behaviors of droplets impacting SLIPS transitions from deposition to rebound and eventually to splash. The higher Weber number of a droplet indicates higher inertia before impacting the surface, which introduces stronger inertial forces to overcome the capillarity of the droplet. Eventually, these properties force the droplet to splash into smaller drops. Compared with many solid surfaces, SLIPS demonstrate a higher probability of droplet rebound, resulting in their advantages in the applications of anti-icing and anti-frosting. In section 3, we analyze the spreading dynamics, retraction dynamics, and contact time of SLIPS. In general, the droplet impacting on SLIPS experiences spreading and retraction processes. During the spreading process, the diameter of the droplet in contact with the surface gradually increases until the droplet spreading diameter reaches its maximum, driven by inertial forces. Subsequently, the droplet enters the retraction process under capillary and viscous resistant forces. The maximum spreading diameter can be scaled as β_max ~ We^1/4 in most conditions. Moreover, the retraction dynamics dominated by viscous forces are affected significantly by the lubricant viscosity. With the increase of the contact angle and the decrease of the lubricant viscosity, the retraction velocity tends to be higher. Further, the contact time is mainly affected by the diameter of the droplet and the lubricant viscosity but is independent of the droplet impact velocity. Compared with superhydrophobic surfaces, the contact time on SLIPS is generally longer owing to viscous retention. In section 4, the different application potentials of SLIPS are systematically summarized. The stability and self-healing of SLIPS are advantageous for the applications, including anti-icing, anti-fouling, fog harvesting, and electricity generators. These applications with SLIPS may revolutionize the modern biomedical devices, solar panels, wind turbines, and small-scale energy generators. Finally, the dynamic characteristics of droplets impacting the SLIPS and the research direction are summarized and prospected. This review provides a comprehensive understanding of the key physical principles underlying the phenomena of droplet impacts on SLIPS as well as further application conditions of SLIPS in energy industries, including industrial anti-icing, defrosting, surface-enhanced heat transfer, and electricity generation from droplets.

Micro-arc oxidation (MAO) is a surface treatment method widely used for fabricating ceramic coatings on light metal substrates. MAO significantly enhances the properties of these metals, including their corrosion resistance, wear resistance, and thermal control capabilities. This paper provides a comprehensive review of recent developments in MAO technology, focusing on the design and application of functional ceramic coatings.
The growth mechanism of MAO coatings involves several key stages: linear voltage increase, local discharge, voltage stabilization, and coating stabilization. In these stages, a ceramic coating with numerous micropores and microcracks is formed, which significantly impact the properties of the coating. By modifying the electrolyte composition, the morphology and properties of the resulting coating can be optimized to satisfy specific requirements.
One of the primary applications of MAO coatings is corrosion protection. The corrosion resistance of MAO coatings can be enhanced by adjusting the electrolyte composition to improve the density and reduce the porosity of the coating. The incorporation of micro-nanoparticles into the electrolyte can further enhance the corrosion resistance of the coating. The addition of certain compounds to the electrolyte during the MAO process can increase the density and thickness of the coating, thereby reducing its porosity and improving its protective properties. Another effective method for improving corrosion resistance is the creation of composite coatings, in which post-treatment techniques are used to seal the pores, thereby enhancing the long-term stability of the coating.
In addition to corrosion protection, MAO coatings provide improved wear resistance and lubrication. The in situ formation of the coating was achieved by adding micro- and nanoparticles to the electrolyte during the MAO process. These particles influence the formation of the coating and contribute to its self-lubricating, high-density, and hard surface properties. Furthermore, post-treatment methods, such as filling the coating pores with lubricating agents or combining the coating with polymer composites, can enhance the wear resistance and lubricating properties of the coating. These post-treatment techniques exploit the porous structure of MAO coatings to improve the adhesion and bonding strength of the lubricants or polymers used.
The thermal protection properties of MAO coatings can be tailored by adjusting electrolyte additives and electrical parameters. By incorporating specific soluble or insoluble additives, it is possible to regulate the optical properties of the coating, such as its solar absorptivity and infrared emissivity. This makes MAO coatings suitable for application in aerospace engineering where heat control is critical. The addition of materials such as metal oxides, which are generated during the MAO process, can further optimize the thermal performance of the coating.
For electrical insulation, high-density MAO coatings with reduced porosity provide excellent dielectric properties. By adjusting the electrical parameters and optimizing the electrolyte composition, it is possible to fabricate coatings with high electrical insulation performance. The porosity, thickness, and density of MAO coatings can be precisely controlled to meet specific requirements for insulation.
Despite these advancements in MAO technology, there are still challenges to overcome. The long-term stability of functional coatings remains a concern because the complex formation process can lead to coating surface porosity and nonuniformity, which may affect the coating performance under extreme conditions. In addition, precise controlling of microstructure and performance of MAO coating—such as porosity, thickness, and density—remains a challenge. Ensuring the comprehensive performance of composite coatings, especially those produced through MAO plus post-treatment processes, presents challenges in different environmental conditions.
In summary, this paper systematically reviews the progress in MAO technology, emphasizing various strategies for optimizing MAO coatings for different applications. The research presented here provides valuable insights into the potential of MAO coatings in a wide range of functional fields. This paper also discusses future directions for improving the performance and expanding the applications of MAO technology, providing a theoretical foundation for further research and practical applications.

Based on the background of the anticipated Industry 4.0 era, the promotion of “Made in China 2025” and the strategy of maritime power, traditional marine anti-fouling coating materials have gradually withdrawn from the historical stage and been replaced by new biomimetic and intelligent marine anti-fouling coating materials. However, a comprehensive and systematic review of new biomimetic and intelligent marine anti-fouling coating materials is still lacking. Therefore, this study reviews the research progress of biomimetic anti-fouling coating materials constructed by biomimetic anti-fouling strategies, such as micro-nanostructure surface, release of green anti-fouling agent, super-slippery surface, dynamic surface, and self-healing. Meanwhile, the research progress of intelligent anti-fouling coating materials formed by intelligent anti-fouling strategies, such as pH, temperature, and light response control, is reviewed. The research progress of synergistic anti-fouling coating materials constructed by the synergistic anti-fouling strategies, namely the combination of biomimetic and intelligent anti-fouling strategies, is also reviewed. Finally, the preparation methods, anti-fouling mechanisms, effects, advantages and disadvantages, and the development trends of the above coating materials are summarized. The emerging biomimetic and intelligent marine anti-fouling coating technology are currently recognized in marine anti-fouling, and has achieved good research results; however, some problems are yet to be resolved. For example, the toxic components of current coating materials have uncertainties and potential risks to the growth and reproduction of marine organisms and marine ecosystems; the surface structure of biomimetic anti-fouling coating is complex; weak anti-fouling durability, stability, and high cost. The response of intelligent anti-fouling coating to external conditions is singular; the anti-fouling stability is not high, and the intelligent anti-fouling evaluation system and mechanism are unclear. Other issues include multi-strategy combined anti-fouling coatings and limited research on the synergistic anti-fouling mechanism between various strategies. Furthermore, the future development direction of anti-fouling coating materials constructed by biomimetic and intelligent multi-antifouling strategies is suggested. In selecting coating materials, the marine environment affinity components are used to replace the toxic components to reduce the risk of toxic substance release into the marine environment; adhering to the principle of "from the ocean, to the ocean" vigorously tap the marine biological resources, extract or synthesize new and efficient bio-antifouling agents to block the related signals and metabolic pathways of fouling organisms to inhibit the deposition and attachment of fouling organisms, rather than direct poisoning, thereby reducing the genetic risk to marine organisms; strengthening the basic research of bionics and biomimetic technology, and studying the microstructure surface, metabolism, and release law and stress behavior of anti-fouling attached organisms to quickly improve the overall design level of biomimetic anti-fouling coating; an intelligent “on-off” anti-fouling system with multiple conditional response was designed, which meets the requirements of convenient and accessible practical application environment and can quickly start and stop according to the specific environment, promoting the broad application of biomimetic and intelligent marine anti-fouling coating materials; increasing the research of multi-strategy combined anti-fouling method systems, such as expanding various anti-fouling strategies and an in-depth study of the synergistic anti-fouling mechanism between various strategies to solve the problem of a single anti-fouling strategy failing to meet the requirements of long-term, stable anti-fouling in the actual complex marine environment, thus ensuring long-term stable and efficient anti-fouling of coating materials. The multi-strategy combined anti-fouling method system will become an important development trend in marine anti-fouling in the future. This study mainly proposes the guiding viewpoint of the method system of the synergistic effect of biomimetic and intelligent multi-antifouling strategies, addressing the issue of limited review articles in the industry. Given the continuous progress of science and technology, the multi-strategy joint anti-fouling method system is expected to promote new breakthroughs in the marine anti-fouling industry in China. Biomimetic and intelligent marine anti-fouling coating materials will become a major development direction of marine anti-fouling in the future. In addition, they have important reference value for the development of national defense and military, marine engineering, maritime transportation, marine fishery, and other fields.

Within the orbital altitude range of 180 km to 650 km, oxygen molecules in the atmosphere tend to decompose into atomic oxygen when exposed to ultraviolet light. Due to its strong oxidizability, atomic oxygen, is capable of causing erosion effects on the surface materials of spacecraft. Complex structural evolutions, such as mass loss, thickness reduction, and changes in surface morphology are involved in this process. So that performance degradation inevitably occurs, highlighting the importance of protecting the surface materials of low-orbit spacecrafts. The adoption of protective coatings is an effective way to improve the atomic oxygen protection performance of materials and ensure the long lifespan and high reliability of low-orbit spacecraft. The research progress of atomic oxygen protective coatings is briefly reviewed, and the factors affecting the performance of atomic oxygen protective coatings are studied. The results show that surface roughness, defects composition and structure of the coating have significant influences on its atomic oxygen protection effect. A rough surface of the coating has advantage in increasing the probability of collisions between atomic oxygen and surface materials, while defects in the coating provide more channels for atomic oxygen and enhance the erosion effects, and the composition and structure of the coating will affect the probability of atomic oxygen reactions. The types of space atomic oxygen protective coatings are investigated, and the characteristics of different types of coatings are analyzed. Atomic oxygen protective coatings can be divided into inorganic coatings, organosilicon coatings, and composite structure coatings. Among them, inorganic coatings are generally solid oxides with a dense structure, and this type of coatings has excellent protective performance but poor flexibility. Organosilicon coatings are mainly composed of elements such as Si, H, C, and O. Good flexibility is achieved through the formation of a polymer-like network structure in organosilicon coatings. When eroded by atomic oxygen, a dense silicon oxide layer appears during the reaction between atomic oxygen and Si atoms located at the surface of coatings, which prevents further erosion. However, under the action of high flux atomic oxygen, the coating surface is prone to shrinkage, resulting in a “tiled” surface and coating cracking. The composite structure atomic oxygen protective coatings can make up for the shortcomings of single-structure coatings and adapt to the needs of different application conditions, however, the performance of this type of coatings is highly correlated with their structure and requires. The coating preparation methods are sorted and summarized, while the advantages / disadvantages and application objects of different preparation techniques are analyzed based on a comprehensive comparison: inorganic coatings with dense morphology can be obtained through magnetron sputtering process, which is mainly suitable for preparing coatings / films on rigid or semi-rigid substrates. Plasma-enhanced chemical vapor deposition in coating preparation corresponds to lower deposition temperature, less thermal damage to substrates. And a wider application range because both inorganic coatings and organic coatings can be achieved in this way. However, due to process limitations, this technology can only be applied to planar substrates and cannot be applied to three-dimensional complex structural parts; ion beam co-deposition can conveniently prepare multi-component composite structure coatings, so it is the main preparation technology for composite atomic oxygen protective coatings; atomic layer deposition has precise coating thickness control, a dense coating structure, no pinholes and other defects, and can form a uniform film on the substrate surface with complex configurations such as steps and grooves. Moreover, it can repair the defects on the substrate surface, therefore having obvious advantages in atomic oxygen protection and achieving good atomic oxygen protection performance at a relatively thin thickness. However, the disadvantage is the low deposition rate, low efficiency, and high stress when preparing thick coatings. Cracks are prone to occur when applied on flexible substrate surfaces. The sol-gel method for preparing coating materials has a low temperature during the process, uniform coating structure, easy control of the reaction process, and low cost. However, in general, the coating thickness is relatively high, requiring tens of microns or more and high quality, which is not conducive to the light weighting of spacecraft. Therefore, it is mainly applied to small structural parts. The precursor photolysis / hydrothermal curing method requires post-treatment such as irradiation and heating when preparing coatings, and the uniformity control is more difficult when implemented on a large area. Therefore, it is suitable for local coating and repair of easily damaged areas on the surface of structural parts. The further development trend of atomic oxygen protective coatings is analyzed and introduced. The research provides the necessary research basis and reference for the atomic oxygen protection of materials for low-orbit spacecraft in China and provides research ideas for the further development of atomic oxygen protective coating technology.

Laser cladding technology is widely used in the field of surface protection and remanufacturing because of its advantages, such as metallurgical bonding between the cladding layer and substrate, high processing efficiency, low dilution rate, and high energy input. It improves the wear resistance and corrosion resistance of the substrate, as well as the life of the cladding layer of the parts. However, instantaneous melting and rapid solidification of the melt pool during the laser cladding process lead to uneven stress within the cladding layer. It has been shown that even if the basic parameters are the same, the scanning paths and scanning time intervals of different lasers significantly influence the temperature distribution, and an uneven temperature distribution further leads to an uneven distribution of thermal stresses, which can cause coating quality issues. To analyze the effect of the scanning paths on the residual stress and tribological properties of the multi-pass laser cladding layer, a multi-pass laser cladding layer of Inconel 718 was prepared on 316L stainless steel using different scanning paths, and the distribution of residual stress in the cladding layer was investigated based on the thermoelastic-plastic model and the residual stress analyzer. The microstructure and hardness distribution of the cladding layer were studied using an X-ray diffractometer, a metallurgical microscope, and a hardness testing system. The tribological properties of the cladding were evaluated using a comprehensive material surface property tester and a laser confocal microscope. The results show that, owing to the difference in temperature cycling during the cladding process, the reciprocating scanning path has the shortest interval between each cladding pass and the lowest surface residual stress. The isotropic and dispersive scanning paths exhibit intermediate surface residual stress levels, while the shrinkage scanning path, which has the largest accumulation of heat in the central region of the cladding layer, exhibits the highest surface residual stress. The isotropic scanning path results in the most homogeneous microstructure due to the differences in temperature cycling during the process. In terms of microstructure, the isotropic scanning path exhibits the most uniform microstructure. Due to the consistent time intervals between each fusion cladding pass, the cooling process remains stable, resulting in minimal changes in crystal size from the cladding layer to the fusion zone. The shrinkage path has the largest accumulation of heat in the fusion cladding layer, and the low cooling rate allowed the crystals more time to grow, which resulted in significant changes in the size of the crystals at the bottom. Owing to the differences between the primary arm spacing and the volume fraction of the Laves phase in the fused cladding, the isotropic scanning path has a uniform distribution with a low content of the Laves phase and the lowest abrasion rate of the fused cladding layer. The reciprocating and dispersive scanning paths have intermediate abrasion rates, while the shrinkage-type scanning path has the highest abrasion rate due to its larger number of Laves phases. Therefore, a reciprocating scanning path should be selected for multi-pass cladding to reduce residual stresses in the cladding layer, and an isotropic scanning path should be selected to reduce the wear rate of the cladding layer. The results of the different scanning paths are expected to provide a theoretical basis for the selection of process parameters in the fields of surface protection and remanufacturing.

Laser cladding (LC) is an advanced material surface-modification technology. Fe313 is a widely used LC material. The addition of WC (hard phase) to the Fe313 powder can enhance and improve the wear resistance of the cladding. However, WC increases the difference in the thermophysical properties inside the cladding and between the cladding and substrate, resulting in cladding defects. Therefore, it is important to monitor the cladding defects and achieve feedback regulation. Acoustic emission (AE) refers to the phenomenon of transient elastic waves emitted due to the rapid release of the local energy of the material. During the LC process, owing to differences in the defect type, size, shape, position, and other factors, each type of defect can generate a unique AE signal. The relationship between the AE signal characteristics and defects was established by extracting the characteristics of the AE signal. Combined with a deep-learning algorithm, an identification method for the LC process state and defects was designed, which can lay a foundation for improving the quality of LC. To conduct the full-cycle monitoring of the LC process, the entire process was divided into five states: powder feeding, melting, cooling, cracking, and porosity. In this study, 45 steel was used as the cladding substrate and 30wt.% WC_p/Fe as the cladding powder. A single-layer, single-pass LC experiment was designed to collect AE signals during cladding. The samples were then cut, ground, and polished. The internal defects in the samples were observed using a super-depth microscope. A quantitative correlation between the number of defects and AE signal was determined by comparing the results of super-depth microscopic images and AE signals. A single-layer multipass LC experiment was designed, and the AE signals of the five states during the cladding process were collected. The AE signals of the five states were analyzed in the time, frequency, and energy domains. Appropriate LC process parameters for repeated tests were selected to obtain and create a dataset. To avoid significant differences in the feature values and discrete distributions between the data samples, the dataset was preprocessed using maximum normalization. An LC state recognition network model based on a Residual Network (ResNet) was designed to determine the LC state, and the AE signal samples of each cladding state containing 1024 signal features were input into the model. Then, the processing was carried out sequentially through convolutional layers, pooling layers, residual modules, and linear layers, and the recognized LC state was the output. Finally, using an LC defect number and duration recognition algorithm, the number of defects generated and the duration of each type of defect were identified. The AE signals of the five LC states were collected in a single-layer multipass LC experiment. From the time-domain perspective, the absolute amplitudes of the five LC states were sorted from largest to smallest as follows: crack, porosity, cooling, melting, and powder feeding states. From an energy perspective, the amplitudes of the five cladding states were sorted from largest to smallest as follows: crack, porosity, cooling, powder feeding, and melting states. In the frequency domain, the frequency bands of the five LC state signal samples were concentrated at approximately 150 kHz, and the identification method of AE signals for LC defects and states based on deep learning could effectively distinguish between the current LC state and the occurrence of defects. The identification accuracy was 97.74% for the unfamiliar datasets. The AE technology, as a nondestructive testing method, can monitor and identify defect signals in the LC process in real time. Deep learning methods, characterized by strong adaptability and high recognition accuracy, can handle complex nonlinear signals. By combining these two methods, new ideas and approaches are provided for the intelligent development of LC technology, and technical support is provided for the feedback control of LC.

The advancement of technology in today’s society has led to higher performance demands for machining tools, and tool coatings have become a primary method for enhancing tool performance. To fully exploit the inherent properties of coated tools, post-treatment is essential. This paper aims to summarize the commonly used post-treatment methods for coated tools, which include sandblasting, polishing, heat treatment, energy field / beam treatments, and others. Sandblasting is the most widely used post-treatment method for coatings. The effectiveness of the post-blasting treatment is determined by three key parameters: grit, pressure, and time. Careful analysis of these variables shows that sandblasting can efficiently remove larger particles from the coated surface while enhancing its overall quality, provided that appropriate conditions are met. Another traditional surface-polishing technique is mechanical polishing, which uses flexible polishing tools, abrasive particles, and other media to modify the workpiece surface. This process effectively removes burrs and larger particles, resulting in a significant reduction in surface roughness. Both sandblasting and mechanical polishing contribute to achieving finer surface finishes on coated materials. Heat treatment is another widely adopted method for both tool treatment and post-treatment of coated tools. During the deposition of tool coatings, the substrate temperature remains low, causing rapid cooling of the coating material. Due to differences in the thermal expansion coefficients between the grains within the coating, thermal stress arises, which can accelerate tool failure. Heat treatment plays a crucial role in relieving some of the strain energy within the coating, adjusting the state of the coating-substrate interface, enhancing microstructural properties, and ultimately improving the performance of coated tools. A recent advancement in post-treatment methods for coatings is the use of energy fields or beam treatments. Energy field treatments include various techniques such as magnetic fields, electron beams, ion beams, lasers, and other similar methods. Compared to mechanical and heat treatments, energy field treatments offer greater controllability and a broader range of action. Research indicates that applying different energy field parameters during post-treatment can enhance not only the surface integrity of the coating but also the bonding strength between the coating and the underlying substrate. This technique involves localized heating of specific areas on the coating using high-density energy, leading to surface remelting and changes in roughness. Additionally, rapid heating and the ensuing energy waves generate thermal stress, which strengthens the coating, substrate, and bonding interfaces. As a result, this process significantly enhances the bonding strength between the coating and the substrate, thereby improving the overall performance of the coating.Although progress has been made in the post-treatment of coated tools, these methods are not yet widely applied in practice, with the exception of polishing. By analyzing the advantages and disadvantages of each post-treatment method, this study clarifies their respective scopes of application, addresses the fragmentation of research in this field, improves understanding of post-treatment methods for tool coatings, and provides a useful reference for the future development of post-treatment technology for coated tools.

In the production process of a hundred-meter-long high-speed railway track, the rolling mill serves as a key component, bearing the effects of alternating high-temperature rolling parts and cooling water. It also faces significant extrusion, shear, and thermal stresses on the surface, resulting in problems such as short service life and severe roller surface wear due to failure. As a primary consumable component in the production processes of many industries, the scrapping a large number of rolls results in considerable waste of energy and resources in China. To repair the surface of scrapped rolls and improve their thermal fatigue performance, we developed the powder composition of iron-based powder, leveraging the good compatibility between the iron-based powder and the matrix material and the reduced cracking during the melting process. Considering the actual production conditions of the rolling mill, selecting an appropriate strengthening element is necessary to improve the performance of the repaired surface. Mo exhibits a good solid-solution strengthening effect and forms carbides, thereby enhancing the strength and wear resistance of the substrate. To further improve the wear resistance of the cladding layer while ensuring good thermal fatigue performance, elemental V was added to improve high-temperature stability, allowing the cladding layer material to maintain good performance at elevated temperatures. A laser cladding technique was used to prepare an iron-based coating using T504 as the base powder, with Mo and V added to the surface of a fatigue- failed 160CrNiMo roller material. The crack propagation rate and mechanism in the base material and cladding layer during thermal fatigue were analyzed using optical microscopy, scanning electron microscopy, and thermal fatigue testing machines. The results show that the average hardness of the cladding layer with Mo and V ratios of 1:0.5, 1:1, and 1:1.5 is 59.2 HRC, 59.9 HRC, and 59.1 HRC, respectively, representing an average increase of 33.4% compared to the substrate; The driving force for crack propagation during thermal fatigue tests primarily arises from the thermal stress generated by cold and hot cycles. After 2000 thermal fatigue testing cycles, the crack length in the matrix material sample measured 11.289 mm. Due to its high carbon equivalent, the brittle phase of eutectic M₇C₃, which contains a higher Cr content than the surrounding material, exhibited a different coefficient of thermal expansion. This mismatch became the main channel for crack propagation during the thermal fatigue testing process, where cracks primarily propagated in a transgranular form. The crack lengths of the samples with added Mo and V mass ratios of 1:0.5, 1:1, and 1:1.5 in the cladding layer were 3.185 mm, 16.596 mm, and 8.401 mm, respectively. The high hardness of the cladding layer, resulting from the addition of Mo and V, increased its brittleness. As the V content increased, the eutectic structure of the cladding layer gradually appeared to break down; the initial boundary became clear and blurred, compromising the integrity of the structure and leading to an increase in the number and length of microcracks. During thermal fatigue testing, the propagation of fatigue cracks was predominantly brittle and transgranular, exhibiting a rapid propagation rate. The sample completed the rapid crack propagation stage after 50-100 cycles. However, appropriate addition of V can improve high-temperature stability and result in shorter cracks. When the mass ratio of Mo to V was 1:0.5, the thermal fatigue performance of the roller material before repair improved by 71.7%. A comparison of the thermal fatigue characteristics of the iron-based coatings with different Mo and V mass ratios provides an experimental basis for selecting iron-based coating systems for roller repair.

Conventional nitride coatings cannot satisfy the growing demand for surface protection. In 2004, Ye Junwei broke away from the traditional alloy design concept and creatively proposed a new material design concept for multi-principal element high-entropy alloys. Over the past 20 years, the elements chosen for high-entropy coating research have mostly been transition metals, and it has been difficult to exceed 1 000 HV. Owing to their unique composition and microstructure, high-entropy alloy nitride coatings exhibit excellent mechanical, wear, and corrosion resistance properties, thus providing prospects for the surface protection of industrial components used in harsh environments. Nano-multilayer structures, as an effective means of tailoring the microstructure and properties of conventional hard wear-resistant coatings, have been applied to the design and preparation of these coatings. In this study, self-organized nano-multilayer multi-element AlCrNbSiTiN high-entropy nitride coatings were deposited via cathodic arc ion plating. A self-organized nano-multilayer structure was achieved by optimizing the process parameters to control the spatial distribution of the plasma components. Nano-multilayer AlCrNbSiTiN / CrN coatings and single-layer CrN coatings have also been synthesized via cathodic arc ion plating. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to study the crystals and microstructures of the coatings. A nanoindentation, a friction and wear tester, and an electrochemical workstation were used to investigate the hardness, friction factor, and corrosion behavior of the coatings. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) were used to observe the wear and corrosion morphologies as well as the compositions of the coatings. The results showed that the CrN, AlCrNbSiTiN, and AlCrNbSiTiN / CrN coatings had face-centered cubic structures. The AlCrNbSiTiN coatings had a self-organized multilayer nanostructure with a modulation period of 12 nm, and the AlCrNbSiTiN / CrN coatings had a multilayer nanostructure with a modulation period of 24 nm. The highest hardness of the AlCrNbSiTiN coatings is 34.5 GPa, with H / E and H³ / E² values of 0.076 and 0.166, respectively. The AlCrNbSiTiN / CrN coating had the lowest friction factor of 0.389, whereas those of the CrN and AlCrNbSiTiN coatings were 0.437 and 0.514, respectively. The AlCrNbSiTiN / CrN coatings show the highest corrosion potential of -47 mV, whereas the AlCrNbSiTiN coatings have the lowest corrosion potential of -157 mV. The AlCrNbSiTiN / CrN coatings had the highest critical pitting potential of 900 mV, which was higher than the 690 mV for the CrN coatings and slightly higher than the 883 mV for the AlCrNbSiTiN coatings. The passivation width of the AlCrNbSiTiN coatings was 943 mV, which was higher than the 66 mV of the CrN (645 mV) and AlCrNbSiTiN / CrN coatings. The corrosion current density of the AlCrNbSiTiN coatings was 2.49×10^-8 A / cm², and the passivation current density was 1.41×10^-6 A / cm², which were less than the corrosion current density of the CrN coatings of 3.04×10^-8 A / cm² and passivation current density of 1.32×10^-5 A / cm². This value was also less than the corrosion current density of the AlCrNbSiTiN / CrN coatings of 5.06×10^-8 A / cm² and the passivation current density of 6.67×10^-5 A / cm². The AlCrNbSiTiN coatings exhibited the smallest pitting holes on the surface. Compared with the CrN and AlCrNbSiTiN / CrN nano-multilayer coatings, the self-organized AlCrNbSiTiN nano-multilayer coatings showed the best comprehensive performance with a hardness of 34.5 GPa, friction factor of 0.514, critical pitting potential of 883 mV, passivation width of 943 mV, and corrosion current density of 2.49×10^-8 A / cm². Based on these results, self-organized nano-multilayer high-entropy nitride coatings can be prepared using arc ion plating technology by regulating the spatial distribution of plasma components. Self-organized nano-multilayer high-entropy nitride coatings exhibit superior mechanical, frictional, and corrosion resistance. This study provides a new approach for preparing nano-multilayer multi-element structured coatings.

Thermal barrier coatings (TBCs) are efficient functional insulation coatings applied to power equipment such as aircraft engines and gas turbines. They have advantages such as low thermal conductivity, good high-temperature phase stability, and fracture toughness. With the continuous enhancement of power systems, key components must often be used in extremely high temperature environments, which can easily lead to the cracking, delamination, degradation, and premature failure of a coating. Therefore, the development of thermal barrier coatings high insulation values and long lives is very important. This article summarizes several typical failure mechanisms of thermal barrier coatings, including failure induced by stress, failure caused by sintering, and failure caused by the infiltration of calcium-magnesium-aluminum silicate (CMAS) and thermally grown oxide (TGO). In order to reduce the residual stress, it is necessary to gradually improve the failure prediction models of TBCs with different preparation processes and different materials, which will improve the reliability and accuracy of the prediction model results. On the other hand, the coating strain tolerance can be increased to release the residual stress, such as by increasing the porosity of the coating and prefabricating cracks in it, which will alleviate the coating stress concentration. In view of the problem of high-temperature sintering, methods to adjust the internal pore structure of the coating by doping metal oxides in the matrix require further study. The thermal-mechanical-chemical coupling effect can be considered to delay the erosion of CMAS, and an in-situ autogenous method can be used to prepare a dense layer, but there have been few studies on this aspect. In addition, a TGO layer with large grain size can be prepared on the surface of the adhesive layer in advance, which can slow down the grain boundary diffusion and limit the growth of TGO by increasing the grain size. Methods have been proposed to reduce the internal porosity of the coating, reduce the difference in interlayer thermal expansion coefficients, and reduce the surface roughness to suppress coating failure. Therefore, the progress on thermal barrier coating research is summarized from two aspects: material selection and the structural design of top coatings. From the perspective of material selection, the problems with using zirconia and some yttrium-stabilized zirconia (YSZ) in long-term high-temperature environments are summarized. In recent years, some advanced coating materials have been developed, including oxide-stabilized zirconia, A₂B₂O₇ oxide, rare-earth tantalite, and self-healing materials. In order to reduce the residual stress, it is necessary to gradually improve the failure prediction models of TBCs with different preparation processes and materials, which will improve the reliability and accuracy of the prediction model results. On the other hand, the coating strain tolerance can be increased to release the residual stress, such as by increasing the porosity of the coating and prefabricating cracks in it, which will alleviate the coating stress concentration. In view of the problem of high-temperature sintering, methods to adjust the internal pore structure of the coating by doping metal oxides in the matrix require further study. The thermal-mechanical-chemical coupling effect can be considered to delay the erosion of CMAS, and an in-situ autogenous method can be used to prepare a dense layer, but there have been few studies on this aspect. In addition, a TGO layer with large grain size can be prepared on the surface of the adhesive layer in advance, which can slow down the grain boundary diffusion and limit the growth of TGO by increasing the grain size. From the perspective of structural design, preparation methods for different coating structures have been introduced. Layered structures, columnar structures, nanostructures, and functionally graded structures are reviewed from the perspectives of their microstructures and corrosion resistance, internal thermal stress, and thermal cycle life values. Finally, the future development directions for long-life thermal barrier coatings are outlined. This review not only discusses the shortcomings of the existing research and direction of future research, but also provides a theoretical basis for the development of a new generation of TBCs with higher corrosion resistances, better thermal insulation values, and longer lives.

Additive manufacturing technology can realize the integral molding of complex components of ceramic materials, but defects exist, including the “step effect” multiphase distribution, and porosity on the surface of the components. Moreover, subsequent precision machining struggles to meet the urgent demand for high-performance silicon-carbide ceramic components for space optical detectors and semiconductor manufacturing equipment. Therefore, this study proposes a novel approach by which to repair surface defects in ceramic additive manufacturing using the chemical vapor deposition (CVD) of high-purity, high-density silicon carbide coatings. However, the proposed method still faces problems of interfacial bonding with the additive ceramic substrate and the growth pattern of the coating. Hence, the effects of the deposition temperature on the interfacial bonding, micromorphology, surface hardness, and machinability of chemical vapor-deposited silicon carbide on additive manufacturing ceramic surfaces were systematically investigated. This study used rapid laser prototyping and the silicone infiltration composite method to manufacture silicon carbide ceramic substrates and prepare silicon carbide coatings via chemical vapor deposition. The silicon carbide coatings were deposited at different temperatures of 1 200, 1 300, 1 400, and 1 500 ℃. The coatings were then deposited on the surfaces of ceramic substrates at the same temperature. The effects of the deposition temperature on the hardness, deposition efficiency, interfacial bonding, microstructure, and processability of the SiC surface coatings were systematically investigated using various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), surface roughness measurements, micro-computed tomography (micro-CT), and scratch tests. The results showed that the hardness of the additively fabricated SiC ceramic was only 1 226 HV_0.5 before any coating was deposited, and the roughness after polishing was 1 980 nm. Because of the presence of multiple phases, the roughness was too high to achieve a mirror effect. At a deposition temperature of 1 200 ℃, a peak of free silicon (Si) appeared in the coating owing to the high precursor gas concentration. However, the temperature was insufficient to promote uniform surface deposition, which resulted in an apparently homogeneous deposition in which free Si atoms in the gas phase were deposited directly onto the substrate. As the deposition temperature increases, the deposition rate accelerates, and the critical nucleation radius of the new phase gradually increases. The critical nucleation free energy also increases, resulting in the formation of larger SiC grains. The Si-C bonds within these grains remained intact, contributing to the overall hardness. However, at an excessively high deposition temperature, pores begin to form between the grains, resulting in low density and high porosity of the substrate and coating. Despite these problems, the silicon carbide coatings deposited at all temperatures formed good bonds with additively fabricated ceramic substrates. Notably, as the deposition temperature reaches 1 400 ℃, the silicon in the substrate begins to evaporate, and defects and porosity appear on the substrate surface. These defects provide additional nucleation points for the coating, and the morphology of the coating at the interface becomes columnar. As the coating grows to a certain thickness, it transforms into a dense structure. The columnar crystals significantly enhance the bond strength of the coating and improve its surface workability, which reduces its roughness to 9.08 nm. After polishing, the coating exhibited a mirror-like finish at all deposition temperatures. Thus, this study demonstrates that the application of CVD SiC coatings can significantly improve the surface quality of additively manufactured ceramics. This approach provides a theoretical basis for engineering applications of high-performance ceramic components in advanced devices.

The automotive part, mold, machine tool, medical equipment, and aerospace industries are involved in the cutting of difficult-to-machine materials. The cutting process is subjected to a strong coupling of force and heat, and a hard coating on the surface of the cutting tool can reduce the cutting force and heat generated during the cutting process. With the continuous development of the high-end manufacturing industry in China, cutting tools will be affected by the lack of toughness of the hard coatings, which could lead to premature damage and even catastrophic fractures in the machining processes of critical components. In recent years, inspired by biomaterials, researchers have devoted themselves to overcome the limitations of mechanical properties, such as the hardness and toughness of conventional materials, and endowing them with special functions through the design of gradient structures. Therefore, this paper summarizes several typical gradient hard tool coatings. The current research status and prospects of gradient hard tool coatings are systematically outlined to provide a reference for the development of high-performance tool coatings. First, the properties of hard coatings and their preparation techniques are introduced. Hard coating materials, such as transition metal nitride coatings, are widely used in machining and forming tool industries owing to their excellent properties, including their outstanding hardness, wear resistance, thermal stability, and corrosion resistance. To meet the growing industrial demands, hard coating preparation technologies have evolved from single and conventional coating preparation technologies to diverse composite technologies. Next, the advantages of the gradient hard coatings are analyzed in terms of the gradient design of the elemental composition, deposition parameters, and gradient design of multilayer structures. Gradient structure design can enable the coating to exhibit one or more unique properties and thereby improve the working efficiency and service life of the coated parts. In terms of composition design and structure optimization, the elemental composition gradient structure can effectively solve the problem of sudden changes in the internal properties of the coating and enhance the matching between the coating and the substrate as well as that between the coatings to thereby reduce the internal stress of the coating and inhibit the generation and expansion of cracks. Compared with the elemental composition gradient coating, the multilayer gradient structure can combine the advantages of the multilayer and gradient structures to improve the comprehensive performance of the coating. Moreover, the multilayer gradient structure is easier to realize. Subsequently, the comprehensive performance of the gradient hard coatings was evaluated in terms of microstructure, static performance, and in-service performance. Owing to the wide variety of materials, structures, preparation processes, and technologies used for gradient hard coatings, analyses of the microstructures and properties of gradient coatings can help select appropriate coatings and preparation processes according to specific application scenarios. The static properties mainly include the hardness, bond strength, and thermal stability of the coating, whereas the service properties focus on the wear resistance of the coating, that is, the machining wear of the coating during the actual cutting process. In terms of the performance evaluation of gradient hard tool coatings, the mechanical properties of the coatings are currently primarily analyzed via experimental intuition. Fast and efficient performance evaluations of coatings via experiments combined with simulation calculations or machine learning methods remains a challenge. Finally, the current state of research and future directions for gradient hard coatings are summarized. Computational simulations and data-driven approaches accelerate and simplify material design and discovery processes. Because both material composition and structure affect their properties, in many cases, the structure and composition of gradient coatings and their properties are complex nonlinear relationships that are difficult to represent via experimental experience or theoretical models. In contrast, machine learning can be used to predict the coating properties as well as the design and optimization of gradient structures by constructing models for the interconnections between the composition and structure to inform the design and optimization of gradient structures. This study focuses on the gradient design of hard tool coatings and their performance evaluation to provide a theoretical understanding of the gradient design and performance evaluation of hard tool coatings.

The rapid development of artificial intelligence technology has led to significant changes and opportunities across various sectors. Machine learning, an important branch of artificial intelligence, can discover laws and patterns from data to make predictions and decisions. Furthermore, it has been widely used in the field of laser cladding in recent years. Laser cladding technology has emerged as a transformative method with numerous advantages, positioning it as a key player in various industrial applications. Its advantages, including high fusion efficiency, optimal material utilization, robust bonding, and extensive design flexibility, render it indispensable for repairing complex surface defects in metal parts. The occurrence of defects during the cladding process can significantly affect the quality and performance of the cladding layer. Ensuring the reliability and repeatability of cladding quality remains a significant challenge in the field of laser cladding technology. In this study, the application of machine learning algorithms in the field of laser cladding defect assessment is explored. A comprehensive and in-depth analysis of common defects and their formation mechanisms in the laser cladding process is provided. The acoustic, optical, and thermal signals generated during the cladding process are summarized, and the corresponding relationships between these signals and the cladding defects are described. Commonly used methods, sensors, and signal characteristics for monitoring the laser cladding process are summarized. Additionally, the classification and features of machine learning algorithms are organized and their use in signal processing is reviewed during the laser cladding process. The classification and characteristics of machine learning algorithms and their applications in laser cladding signal processing are summarized. Machine learning algorithms have been employed in detecting defects in laser cladding, typically by constructing datasets from features extracted from collected signals, the cladding process, and defect characteristics. These algorithms are used to establish relationships between the signals, defects, and the process. However, most current studies on laser cladding monitoring focus on a single pass or a small area of the cladding layer. The use of such small datasets can lead to model overfitting, thereby reducing the accuracy of defect detection. Nevertheless, the application of these algorithms facilitates the introduction of a dynamic feedback control mechanism that optimizes the cladding process and effectively mitigates defects. The convergence of laser cladding and machine learning has emerged as a vibrant area of research, tackling crucial issues and expanding the limits of quality assurance and process optimization. Researchers, both domestically and internationally, have examined pores, cracks, and other defects at various scales through experiments and simulations. However, the mechanisms behind these defects and their impact on the quality of cladding are not yet fully understood. There is a need for more comprehensive methods to study the laser cladding process. Developing a quantitative evaluation system that links the laser cladding process, signal data, and defect quality is a critical challenge in ensuring the reliability of laser cladding quality. Currently, various sensors, including acoustic, optical, and thermal types, are utilized to monitor the laser cladding process. These sensors aid in examining the relationship between the process signals, defects, and quality. However, the limitations in sensor accuracy and the efficiency of defect feature extraction pose challenges in establishing a precise process-signal-defect relationship. The predominant machine learning algorithms used in current research are supervised learning algorithms. However, unsupervised and semi-supervised learning algorithms, which require less data labeling, are drawing attention in the fields of laser melting and cladding process monitoring, demonstrating significant potential. This review emphasizes the current research hotspots and directions for applying machine learning methods in laser cladding.

Thermoplastic polymers such as polyethylene terephthalate (PET) and their glass-fiber-reinforced composites are widely used in electrical appliances because of their excellent electrical insulation and environmental friendliness. Aluminum alloyhas good electrical conductivity and environmental adaptability, and it is often used as the conductive part of electrical devices. Currently, the interface strength of PET-metal bonding parts is low, and there are few studies on the combination of 30 wt.% GF / PET-Al injection molding parameters. In this paper, the surface of metal Al was sandblasted first, and then, ultrasonic cleaning was conducted with deionized water / alcohol for many times. Meanwhile, the silane coupling agent (KH-892) was hydrolyzed to break the silicon-oxygen bond in the silane coupling agent, generating a silicon hydroxyl compound, and finally, a silicon alcohol solution was generated. The 2024 aluminum alloy after cleaning was infiltrated into the silicon alcohol solution, and then, the infiltrated aluminum alloy was placed in the oven to cure so that the metal surface formed a silane film. Finally, 30 wt.% GF / PET-2024Al composite joint was prepared by injection molding. The standard orthogonal experiment table was first referred to and the pre-experiment was carried out for studying the effect of injection molding parameters on the interface bonding strength. The orthogonal experiment design of injection molding parameters was conducted. The mechanical test of each group of test samples was conducted, and the obtained data were analyzed by variance analysis. The effects of melt temperature, mold temperature, injection time, holding time, and holding pressure on the interface strength of PET-2024Al bonding parts were analyzed. The response surface model was established, and the NSGA-II optimization algorithm was used for solving the optimal injection parameters. The 2024Al metal interface was treated by silane coupling agent. The tensile shear test was conducted on the large sample that was closer to the actual injection molding process and reflected the injection molding defects. The effect of silane coupling agent concentration on the bonding strength was studied, and subsequently, the response surface model was established. The NSGA-II optimization algorithm was used for solving the optimal injection parameters. The 2024Al metal interface was treated by silane coupling agent. The tensile shear test was conducted on the large sample was closer to the actual injection molding process and reflected the injection molding defects. The effect of the silane coupling agent concentration on the bonding strength was studied. The tensile shear strength of the joint coated with 1wt % KH-892 silane reached 12.79 MPa, which was 84.3% higher than that of the sandblasted sample without KH-892 coating. X-ray photoelectron spectroscopy (XPS) was used for revealing the formation of Si-O-Al bonds between silane and aluminum alloy under high temperature curing. Fourier transform infrared spectroscopy (FTIR) was used for revealing the formation of strong hydrogen bonds between silane and PET molecular chains. Finally, scanning electron microscopy (SEM) and energy dispersive spectrometery (EDS) were used to reveal the difference between the interface fracture modes and the surface morphology of PET-aluminum alloy bonding parts caused by different concentrations of silane coupling agent KH-892. Finally, the optimal injection molding parameters were obtained. KH-892 was found to promote the formation of Si-O-Al bonds between PET-2024Al and the formation of hydrogen bonds, thereby resulting in an increase in interfacial strength.

Aluminum-based intermetallic compounds are recognized for their excellent high-temperature mechanical properties, high resistance to oxidation and corrosion at elevated temperatures, and low density. These characteristics make them suitable for a broad range of applications, including protective coatings and structural components in aerospace and other industries. High-energy-beam additive manufacturing technologies, such as laser and electron beam melting processes, are effective for the rapid fabrication of complex metal structures. However, depositing aluminum-based intermetallic compounds remains challenging due to their complex phase structures and inherent brittleness, which often lead to flaws and defects, particularly cracks. Cold spraying, a process characterized by low processing temperatures and high deposition rates, shows significant potential for the low-heat-input fabrication of aluminum-based intermetallic compounds. This paper summarizes and analyzes recent advancements in the preparation of aluminum-based intermetallic compounds using cold spraying. Effects of powder design and fabrication routes on deposition behavior and deposit properties are discussed. These routes include intermetallic compound powder deposition, mixed elemental metal powder cold spraying followed by heat treatment, and cold spraying of mechanically ball-milled pseudo-alloy powders with subsequent heat treatment. First, the deposition behavior of intermetallic compound powders is reviewed and discussed. In the cold spraying process, successful deposition and bonding of spraying particles rely on plastic deformation induced by particle impact. However, due to the intrinsic brittleness of intermetallic compounds at room temperature, it is difficult to deposit particles directly using intermetallic compound powders as feedstock. In practice, when relatively soft materials are used, only a single layer of intermetallic particles can be mechanically embedded into the substrate layer. Subsequent spraying does not contribute to building up of the deposit because achieving successful bonding between intermetallic particles is highly challenging. Although high gas temperatures, even up to 1 000 ℃, are used to soften intermetallic particles, depositing a thick, high-quality deposit remains elusive. Thus, preparing intermetallic deposits using intermetallic feedstock powders continues to be a challenge. To address this issue, an alternative strategy involving the formation of intermetallic compounds during or after deposition has been extensively investigated. Following this strategy, mechanically mixed powders containing aluminum (Al) and other elemental powders, such as iron (Fe), nickel (Ni), or titanium (Ti), are used as feedstock materials. Due to the excellent plastic deformability of elemental metal powders, deposits containing mixed elemental metal particles can be easily deposited by cold spraying at relatively low gas temperatures and pressures. Post-spray heat treatment or annealing is then performed to activate interdiffusion between the Al and Fe / Ni / Ti phases, facilitating the formation of intermetallic compounds. However, the higher deposition efficiency of Al powder compared to Fe / Ni / Ti powders often results in cold-sprayed composite deposits with a higher Al content than the feedstock powder, complicating precise control of the chemical composition. This challenge is particularly pronounced when the feedstock powder contains more than three elemental metal powders. Additionally, during heat treatment, the long diffusion paths required for intermetallic compound formation frequently lead to the creation of numerous Kirkendall pores, and achieving a single intermetallic phase proves difficult. To overcome these challenges, a method involving the cold spraying of mechanically milled pseudo-alloy powders, followed by heat treatment, is proposed. By controlling the intensity and duration of high-energy ball milling, pseudo-alloy powders with alternating submicron lamellae of various metals can be prepared from mechanically mixed metal powders. The composition of the pseudo-alloy powder can be precisely controlled by adjusting the proportions of the raw materials. Moreover, the pseudo-alloy powder retains the plastic deformation capability of the original elemental metals, ensuring efficient deposition during cold spraying. The fine microstructure of the alternating submicron metal lamellae significantly shortens diffusion paths during heat treatment, effectively mitigating the formation of Kirkendall pores in the deposit. Finally, the effects of post-treatments such as friction stir processing (FSP) and hot isostatic pressing (HIP) on the microstructure and properties of the deposit are summarized. FSP treatment greatly refines the microstructure of deposits sprayed with mechanically mixed elemental metal powders, resulting in structures featuring alternating submicron metal lamellae and partially formed intermetallic compounds. This refinement significantly shortens diffusion paths between phases and prevents the formation of Kirkendall pores. However, it is challenging to process parts with complex shapes using this method. In contrast, HIP applies isostatic pressure during treatment, closing Kirkendall pores and making it suitable for parts with complex geometries. Overall, cold spraying of mechanically mixed elemental metal powders followed by HIP treatment, as well as cold spraying of mechanically milled powders combined with subsequent heat treatment, have been shown to produce aluminum-based intermetallic compounds with low porosity and high hardness. By comparing and analyzing the advantages and limitations of different technological routes, this study aims to provide guidance for the cold-spraying additive manufacturing of aluminum-based intermetallic compounds.

It is often the case that extreme conditions are frequently encountered in high-tech equipment, where conventional materials often prove inadequate inmeeting the requirements of intended application. It is therefore imperative that ultra-high-performance materials and technologies be developed to tackle these challenges. In view of the demand for lubricating and wear-resistant surface technology in the development of national frontier equipment under harsh conditions, this study presents a review of recent advancements in this special materials field, with particular focus on the aerospace and nuclear energy sectors. It takes the adhesive solid lubricant coatings developed by our team as object, emphasizing key common technical challenges and addressing practical engineering issues. Including key technologies such as the modification of tough and strong integrated basic resins, the improvement of atomic oxygen resistance by POSS modified resins, the design and adaptive control of lubrication components over a wide temperature range, the design of surface and interface of coatings resistant to special media, and the control of system compatibility. Additionally, a compilation of representative products developed based on this basis is listed, together with an illustration of their exemplary applications in addressing friction-related challenges under extreme conditions within high-tech equipment domains. The application in key components of aircraft and aviation engines, in key components of rockets and satellites, especially in the docking mechanism of space stations, has solved the lubrication and wear problems of components under many extreme conditions in aerospace. This underscores the indispensable and crucial role played by advanced lubrication and wear-resistant surface engineering technologies in driving forward national advancements in high-tech equipment. Finally, considering future developmental requirements for cutting-edge manufacturing at a national level, potential directions for further advancing extreme condition lubrication and wear-resistant surface engineering technologies are explored. This article provides a comprehensive understanding of the demand for extreme condition lubrication and wear-resistant surface engineering technology in the national high-tech field, promotes the high-tech application of related technologies and products, and develops higher limit performance lubrication and wear-resistant surface engineering technology for future high-tech equipment needs. It offers a valuable reference point and provides guidance significance on these matters.

Currently, few studies have addressed three-dimensional numerical models that consider oil film thickness, hydrodynamic pressure, and cavitation effects. Notably, a research gap exists in exploring the influence of texture distribution modes on lubrication performance. Therefore, advancing relevant research is imperative. To investigate the impact of surface texture distribution modes on lubrication performance under fluid lubrication conditions, this study aims to establish a three-dimensional calculation model for non-uniform texture distribution while accounting for oil film thickness. The model will utilize Computational Fluid Dynamics (CFD) methods, along with a User Defined Function (UDF) and dynamic mesh technology, to systematically explore how texture area density and distribution modes affect key parameters, including friction factor, oil film thickness, pressure distribution, and gas phase distribution. The numerical simulation results indicate that, under constant external load conditions, increasing texture area density leads to a decrease in the spacing of uniformly distributed textures. This phenomenon enhances the hydrodynamic lubrication effect while concurrently inhibiting the cavitation effect, resulting in a thinning of the oil film and an increase in the friction factor. In contrast, non-uniformly distributed textures enhance the hydrodynamic lubrication effect and weaken the suppression of the cavitation effect. This leads to an increase in the bearing capacity of the oil film, thickening of the oil film, a decrease in the velocity gradient, a reduction in shear stress, and a lower friction factor. Additionally, non-uniformly distributed textures alter pressure distribution, forming a localized high-pressure zone. The high-pressure zone generated by gradually sparse textures is larger and positioned closer to the symmetry center compared to that created by closely distributed textures. In terms of gas volume, the cavity volume associated for sparser distribution textures is greater than that of more closely arranged textures. Overall, lubrication performance is superior for sparser distribution textures compared to closely arranged ones. When the texture area density is 14.14%, the friction factor for sparser distribution textures is reduced by 26.5% compared to uniformly distributed textures. Simultaneously, the air volume fraction increases by 22.9%, and oil film thickness increases by 53.5%. For closely distributed textures, the friction factor decreases by 24.2%, the air volume fraction increases by 16.7%, and the oil film thickness increases by 32.5%. According to the experimental results, as rotational speed increases, oil film thickness across all three texture distributions demonstrates an upward trend, enhancing lubrication at the friction interface and reducing the friction factor. Notably, the non-uniformly distributed texture exhibits greater oil film thickness and a smaller friction factor than the uniformly distributed texture. This finding suggests that non-uniformly distributed textures can effectively improve lubrication performance. Furthermore, sparser distribution textures outperform closely arranged textures in overall performance, corroborating the simulation results. In this study, a UDF program was employed to control and compute in FLUENT software, considering the influence of changes in oil film thickness under constant load conditions. By analyzing the impact of surface texture distribution modes on lubrication performance, this study provides new insights and theoretical references for optimizing texture distribution design and enhancing research methodologies related to texture performance.

Hydraulic actuators are widely used in aircraft wings, doors, and landing gears. The reciprocating seal is a common seal type. Seal failure can significantly affect aircraft mission execution and flight safety. The surface roughness of the seal pair is a major controllable parameter in engineering and greatly influences sealing performance. Therefore, analyzing the effect of surface roughness on the sealing performance of actuators is both theoretically and practically significant. The Al₂O₃ oxide film formed on the surface of aluminum alloys after hard anodic oxidation has certain wear resistance, insulation, and corrosion resistance, making it widely used in aviation hydraulic systems. However, the hard anodized film (hard oxygen film) has problems such as high porosity, roughness, and friction coefficient, which can exacerbate wear and tear on the friction mating surfaces, severely limiting its practical service. Hard anodization of aluminum alloy is a dynamic process involving the formation and dissolution of the film layer in a low-temperature sulfuric acid solution. The film layer is generally divided into a compact layer adjacent to the substrate and a looser layer extending outward. Consequently, the surface hardness is low, and the roughness is inadequate. An in-situ synthesis technology is utilized to enhance the surface roughness of the aluminum alloy hard anodized film and improve its friction-reducing performance, thus meeting the service requirements of the new generation of aeronautical actuators for weight reduction and high mobility. First, wed added 15-20 mL / L of PTFE (Polytetrafluoroethylene) concentrated dispersion liquid and a proper amount of composite surfactant into the anodizing bath liquid. We then stirred it for 30 min using a direct current constant current method at a current density at the beginning of hard anodic oxidation of 0.5-1 A / dm². The current density was increased every 5 min until the desired current density was reached, where the film thickness required by the process was maintained to complete the anodic oxidation. During the hard anodizing of the aluminum alloy composite PTFE, negatively charged PTFE particles were pretreated with a composite surfactant and moved towards the surface of the aluminum alloy substrate under the action of an external electric field. As the oxide film continuously formed, the PTFE particles were absorbed and encapsulated in the film. The pores of the film layer were nearly filled with PTFE, where the PTFE was fully dispersed in the oxide liquid. The particles have a heat absorption function, effectively dissipating Joule heat from the substrate surface. Reducing the dissolution rate of the composite oxide film facilitated the formation of a low porosity and relatively compact film layer. This involved preparing the aluminum alloy composite PTFE hard oxygen film layer and detecting and analyzing its hardness, thickness, cross-sectional morphology, and phase composition. The relationship between the polishing amount and the roughness of the film was analyzed by using a three-dimensional roughness tester. Finally, the wear resistance of the friction pair with different roughness levels was verified through engineering simulation using an abrasion tester. The results showed that the hardness of the aluminum alloy composite PTFE hard oxygen film was higher than that of the hard anodized film, with surface roughness reduced from Ra2.4 μm to Ral.0 μm. Following 10 μm polishing, the surface roughness was less than Ra0.2 μm. Under the same load and time conditions, the friction coefficient of the composite film pair and the wear rate of the friction pair were both lower, at 0.08 and only 2.10 × 10^-7 mm³ / Nm, respectively. No peeling was observed in the product’s functional test, and the wear amount was minimal, meeting the product’s performance requirements. In addition, the product (aluminum alloy actuator parts with composite PTFE hard oxygen film) exhibited a self-polishing effect during actual use, which helps shorten the production cycle and significantly reduces costs. The friction and wear behaviors of hard oxygen film layers and composite PTFE hard oxygen film layers were compared and analyzed using the friction and wear pair of a piston (7075)-sealing ring (4FT-32) in an aeronautical hydraulic actuator. This analysis provides data and testing support for the design and treatment of aluminum alloy cylinder-piston pairs and other relevant friction pairs with different application requirements, facilitating the engineering implementation and application of friction pairs in actuating system components.

With the continuous advancement of technology, the requirements for the processing accuracy of optical components in fields such as advanced optics and integrated circuits have gradually increased. From the initial nanometer-level precision to the current pursuit of sub-nanometer-level precision, this transition represents not only an extreme challenge to technology but also necessary support for the future development of science and technology. However, faced with such stringent requirements, current mainstream traditional processing technologies, such as chemical mechanical polishing (CMP), fluid jet polishing (FJP), magnetorheological finishing (MRF), and ion beam polishing (IBP), despite their significant application effects in their respective fields, all have insurmountable limitations. These traditional technologies often struggle to achieve the goal of manufacturing atomically smooth surfaces while ensuring high efficiency. Therefore, manufacturing optical components with sub-nanometer roughness and low subsurface damage while ensuring processing efficiency has become a critical technical challenge in the field of ultraprecision manufacturing that must be urgently addressed. In this context, gas cluster ion beam (GCIB) technology, as an innovation and upgrade to traditional ion beam technology, is gradually emerging in the field of ultraprecision processing owing to its unique processing mechanism and excellent performance, demonstrating significant application potential. Therefore, it is necessary to discuss the principles, irradiation characteristics, and potential applications of GCIB technology. Herein, first, the principles of GCIB technology are explained, and the unique irradiation characteristics of GCIB technology are elaborated. GCIB is an ion beam processing technology based on gas clusters, which are tiny clusters composed of tens to thousands of atoms or molecules. This technology first condenses gas molecules into microclusters through supersonic expansion and then forms an uncharged GCIB through ionization, acceleration, focusing, and neutralization. During processing, these ions strike the workpiece surface at a certain speed and remove the material through physical sputtering to achieve polishing, etching, and other purposes. Compared with traditional ion beam technology, GCIB technology has a series of unique irradiation characteristics that endow it with significant advantages in the field of ultraprecision processing, such as low energy per atom, high sputtering yield, lateral sputtering effect, and dense energy deposition. Based on these characteristics, GCIB technology has broad application prospects in fields such as polishing, etching, thin-film deposition, and secondary ion mass spectrometry (SIMS). To systematically study GCIB technology, this research summarizes its application status in different fields. In the field of polishing, utilizing the low-energy and high sputtering yield characteristics of GCIB enables high-precision surface polishing. In the field of etching, GCIB technology exhibits excellent etching accuracy and controllability, enabling precise etching at the micrometer or even nanometer scale. In the field of thin-film deposition, precise deposition of various types of thin films can be achieved by adjusting parameters such as the composition and energy of GCIB. This deposition method not only has high deposition rates and uniformity but also enables precise control and modification of the films. In the field of SIMS, GCIB technology can also be used as an excitation source to analyze the elemental composition and distribution of materials. Finally, this research discusses the shortcomings and future development directions of GCIB technology. As an emerging technology, existing research has only validated the effectiveness of GCIB technology in laboratory environments and has not proven the feasibility of GCIB processes in actual manufacturing. Additionally, the production cost of GCIB equipment is relatively high, and while its processing efficiency is better than that of IBP, it is still lower than those of CMP and MRF. Therefore, future efforts are still needed to optimize equipment, reduce costs, and improve processing efficiency.

This study explores the tribovoltaic effect and its applications in energy harvesting and smart sensors. The tribovoltaic effect occurs when a sliding motion at a semiconductor heterojunction interface generates friction, which excites electron-hole pairs at the interface. Under the influence of an electric field at the semiconductor interface, these electron-hole pairs undergo directional migration, generating a direct current (DC), a process referred to as the tribovoltaic effect. Devices that harvest mechanical energy based on the tribovoltaic effect are known as tribovoltaic nanogenerators (TVNGs). TVNGs can directly output DC and exhibit low-impedance output characteristics, making them a subject of widespread interest. This paper first introduces the meaning of the tribovoltaic effect and summarizes the key scientific issues involved in its research: the mechanisms of electron-hole pair excitation and the formation of the interface electric field. These issues are critical for understanding the potential of the tribovoltaic effect and for optimizing the performance of TVNGs. Specifically, this research identified that the interaction effect in energy harvesting and smart sensing, with a particular focus on optimizing the TVNG performance. This study discusses the relationship between semiconductor properties and frictional forces that play a significant role in the excitation of electron-hole pairs, while the interface electric field is crucial for the separation and migration of these carriers. Understanding these mechanisms is essential to improving the efficiency and stability of energy conversion in TVNGs. Next, this study explores the applications of the tribovoltaic energy transmission laws involved in the tribovoltaic effect and highlights several challenges, including tribological issues and surface/interface engineering problems. This study proposes that the asymmetry in the geometric structure of materials and friction-induced asymmetry at the interface can significantly contribute to the tribovoltaic effect. These factors were hypothesized to influence the output efficiency and performance of TVNGs, suggesting that a more thorough understanding and control of these variables are necessary to optimize the device performance. This study also emphasized the importance of surface modification techniques and the impact of material properties on the tribovoltaic effect. By altering the surface structure and interface properties of materials, for instance, through doping or chemical treatments, it is possible to enhance the energy-harvesting capacity of the tribovoltaic effect. Furthermore, this study suggests that advancements in tribological research, including the understanding of friction and wear at the interface, are essential for optimizing TVNGs for real-world applications. By improving the surface roughness, frictional behavior, and chemical interactions at the interface, it is possible to maximize the efficiency of the tribovoltaic energy conversion process. Finally, this study discusses future research directions for the tribovoltaic effect, predicting that its study will become increasingly diversified and intelligent. The future of tribovoltaic research will focus on material optimization, specifically enhancing the stability, output power, and durability of TVNGs. These advancements are expected to be key factors driving the development of TVNGs, enabling their widespread use in practical applications. The future of tribovoltaic technology also lies in its potential to play a critical role in smart sensors, environmental monitoring, and wearable devices, with applications extending to self-powered systems and energy-efficient technologies. By improving the material properties and optimizing the overall performance of TVNGs, the tribovoltaic effect is expected to contribute significantly to the development of next-generation energy-harvesting devices. In conclusion, the tribovoltaic effect holds great promise for energy harvesting and smart sensor applications. Future research efforts will focus on improving the performance, stability, and durability of TVNGs, which are crucial for their practical deployment in various industries. The ongoing advancements in materials science, surface engineering, and tribological research are essential for achieving these goals and ensuring the successful integration of tribovoltaic technology into real-world applications.

High-entropy alloy, which is a new type of multi-component metallic material, has been widely studied as a new concept alloy because of its unique composition and microstructure. Given the high cost of preparing high-entropy alloys, high-entropy alloy coatings can be used to bring out the excellent performance of these alloys and are more economical and practical. Because of their high strength, good wear resistance, corrosion resistance, high-temperature stability, and other properties, high-entropy alloys have been used in aerospace, medicine, electronics, and other cutting-edge fields, with promising prospects for future applications. Recently, AlCoCrFeNi high-entropy alloy coatings with body-centered cubic (BCC) structures have been receiving increasing attention in applications because of their excellent high-temperature mechanical properties, high strength, and low cost. In this study, the development status of three typical methods of preparing AlCoCrFeNi high-entropy alloys for coating wear resistance have been studied, reviewing two methods of improving coating wear resistance through modification and three post-processing methods for strengthening wear resistance. In terms of preparation technology, AlCoCrFeNi high-entropy alloy coatings are mainly prepared by plasma-spraying, supersonic flame-spraying, laser cladding, and other processes. The prepared coatings show better thermal stability and wear-resistant properties at high temperatures. The hardness and wear resistance of high-entropy alloy coatings are enhanced as the molar amount of the alloying principal element, Al or Fe, increases in the coating. In terms of compositional modification, the wear-resistant properties of the coatings are affected by the composition of the main elements and elemental molar ratio. Therefore, the wear-resistant properties of high-entropy alloy coatings can be improved by introducing carbide reinforced phases (WC, TiC) and the addition of other elements (Si, Ti, Mo, V, et.al.) to enhance the wear-resistant properties of the coatings. The three post-treatment methods of laser remelting, annealing, and inductive remelting can effectively reduce the defects of high-entropy alloy coating, better combine the coating and the substrate, reduce the porosity, and improve the wear-resistant performance of the coatings. Finally, considering the performance characteristics of AlCoCrFeNi high-entropy alloy coatings, the development direction of AlCoCrFeNi high-entropy alloy coating performance enhancement is prospective. First, to optimize the coating process parameters, an artificial neural network method is used to determine and obtain the coating with the best performance. The combination of heat treatment process technology and optimization analyses including the response surface method is conducive to the study of the comprehensive performance of high-entropy alloy coatings, playing a role in numerous fields. Second, based on the characteristics of the AlCoCrFeNi high-entropy alloy and its application environment, we chose to introduce a reinforcing phase or add other elements to compensate for the performance defects of a single material and enhance its performance. Third, heat treatment, remelting, and other post-processing techniques were used to reduce or even eliminate the pores, cracks, and other defects in the coating and further enhance the mechanical properties of the coatings.

3D-printed silicon carbide (SiC) ceramics have excellent qualities such as high strength and temperature resistance and they permit flexible molding of complex shapes, leading to their wide use in energy processing and advanced aerospace applications in recent years. However, they have poor surface abrasion resistance. Using atmospheric plasma spraying (APS) is an economically feasible method for applying high-temperature abrasion-resistant coating on the surface of parts. Among the common self-lubricating wear-resistant coatings, YSZ coating, with its excellent high-temperature stability and oxidation resistance, is generally used in high-temperature environments. However, to improve the performance of the spraying process and reduce friction, a second phase is often added. This paper proposes (1) doping the coating with both low- and high-temperature lubricants to enable wide-temperature lubrication, (2) adding alumina to reduce the melting point of the powder and improve the coating densification, and (3) using a sol-gel-coated powder to improve the bonding between the base and second phases of the coating. In this study, three composite powders with different compositions of YSZ-Al₂O₃-CaF₂-C were prepared using the sol-gel method and centrifugal atomization drying. The corresponding composite coatings (Ca0C0, Ca5C10, and Ca10C5) were deposited on the surface of 3D-printed SiC ceramics using the APS technique. The microstructures, friction properties, and wear mechanisms of the composite coatings were studied at room temperature and 600 ℃. The results show that the coatings have a typical laminated structure. Both the coatings and abrasion marks were primarily composed of YSZ, Al₂O₃, and m-ZrO₂ phases, with CaF₂ and C phases in Ca10C5 and Ca5C10 coatings. No other chemical reactions occurred during the coating application or owing to friction. The Ca0C0 coatings without CaF₂ and C lubrication phases had the highest hardness, lowest wear rates, and largest friction factor at room temperature and 600 ℃. The strong bonding of the coating to the friction partner at 600 ℃ led to a friction coefficient of more than 1. The stabilized friction factor of Ca10C5 and Ca5C10 coatings were, respectively, 0.239 and 0.130 at room temperature and 0.175 and 0.288 at 600 ℃. The friction factor of Ca5C10 and Ca10C5 coatings considerably reduced upon the addition of CaF₂ and C lubrication phases at both room temperature and 600 ℃, reflecting improved self-lubricating properties. However, the addition of the lubrication phases led to a decrease in the hardness of the coatings and an increase in the porosity defects inside the coatings, accompanied by an increase in wear rate. The Ca5C10 coatings with higher C additions were more prone to abrasive debris generation because of the higher volume fraction of C and lower hardness, resulting in higher wear rates. Based on the abrasion mark morphology, the wear mechanism of the coating was concluded to be primarily adhesive and abrasive. The YSZ-10Al₂O₃-10CaF₂-5C coating had a lower friction factor and wear rate (1.02×10^-5 mm³ / (N·m) at room temperature and 0.84×10^-5 mm³ / (N·m) at 600 ℃) compared with YSZ-10Al₂O₃-0CaF₂-0C and YSZ-10Al₂O₃-5CaF₂-10C coatings in this study. This implies that YSZ-10Al₂O₃-10CaF₂-5C coating has good self-lubricating and wear-resistant properties and can well improve the surface properties of 3D-printed SiC.

The number of criminal cases involving metal objects, such as controlled knives, has gradually increased in recent years. Perpetrators frequently leave fingerprints on metal surfaces, such as stainless-steel door handles, tools, and knives, which can provide crucial evidence. Traditional methods for developing latent fingerprints on metal surfaces include powder, laser, multiband light-source, suspension development, smoke, and high-voltage electrostatic methods. When traditional methods are used to reveal fingerprints on metal surfaces, the ridge lines of the fingerprints often visually interfere with scratches on the metal surface, which can affect the clarity of the fingerprint display. Furthermore, these methods require high equipment standards and are challenging to operate onsite, making them difficult to be implemented widely by local public security organizations. The vacuum metal deposition (VMD) exhibits several characteristics that make it highly sensitive and versatile. One of its key advantages is its ability to preserve DNA and other biologically active components in fingerprints, making it suitable for various applications. VMD is widely used to reveal the latent fingerprints of nonpermeable and semipermeable objects, and it also has a significant effect on aged and problematic latent fingerprints. The handprinted lines are clear and coherent, displaying significant contrast and detailed features. The advantage of VMD lies in its strong sensitivity and effective development of potential fingerprints on challenging materials that conventional methods struggle to process, thus playing a crucial role in critical and complex cases. According to the specifications for producing handprinted samples, latent fingerprints were stamped on brass, red copper, 304 stainless steel, and aluminum alloys. First, this study examined how the combination of two sprayed metals, arranged according to their relative atomic masses, affected the appearance of handprints. Based on this premise, the effects of the quantity and sequence of the sprayed metal on the appearance of the handprints was further investigated. Finally, the effect of the remaining time of latent fingerprints on the development of fingermarks on the four metal objects was examined through statistical analysis. This includes the display rate, average score of the developing effect, and number of latent fingermarks corresponding to the grade score of the development effect. In the experiment, silver and zinc were the highest-quality combinations of metals sprayed on brass, red copper, and 304 stainless steel. For the spraying process, 10 mg of silver and 100 mg of zinc were applied in order of silver followed by zinc, which yielded the best results with latent fingerprints. Gold and zinc were the highest-quality combinations of metals sprayed onto aluminum alloys. For the spraying process, 4 mg of gold and 100 mg of zinc were selected in the sequence of gold followed by zinc; this sequence yielded the best-quality latent fingerprints. Differences in the surface structures of metal objects resulted in varying adsorption capabilities for the different sprayed metals. In addition, the contrast in the color background on different metal substrates caused the combination of zinc / silver to have an optimal effect on brass, purple copper, and 304 stainless steel, whereas the combination of zinc / gold yielded superior quality on aluminum alloy substrates. Moreover, the appearance rate of latent fingerprints on the four types of metal objects gradually increased on days 1, 4, and 7. VMD effectively revealed latent fingerprints on metal objects within a retention period of seven days. In addition, the quantity of sprayed metal, combination of different sprayed metals, sequence of sprayed metals, and remaining time of latent fingerprints influenced the display rate and the developing effect of potential handprints on metal objects. VMD has a significant advantage in developing latent fingerprints on metal objects and serves as a valuable alternative to existing development methods.

Thermal protective coating materials and engineering technology for high-speed airborne missile body structures play an important role in the missile development, batch production & delivery, as well as operation and maintenance and combat effectiveness. The mission profile and life profile of such large quantity of products have the characteristics of harsh service environment, high maintenance requirements, etc., which makes the batch production & delivery of such products different from conventional surface coating technology for common space vehicles, box-type or barrel-mounted strategic/tactical missiles, common machinery, ships and other equipment and facilities, it also different from laboratory material preparation, testing and characterization. In order to achieve advanced performance and stable mass batch production & delivery of high reliability products, this paper aims at many difficulties and engineering problems faced by the independent engineering development of thermal protection of the product structure, such as various product specifications, complex morphology, large quantity, difficult construction with existing coating materials and processes, long cycle, difficult quality monitoring, frequent failures and cost constraints, a series of application researches on surface engineering technology have been carried out. Based on in-depth analysis of the characteristics of the product structure, operation, service & maintenance, the mission & life profile, the application research and engineering practice on special engineering technologies directly affecting mass batch production & delivery are discussed. The contents discussed are selection of engineering material system for external thermal protective coating and internal thermal insulation coating, research and development of thermal-resistant coating production technology of mass and high efficiency, and physical and chemical inspection, process inspection and delivery inspection related to product quality control, failure handling. The experiences described in this paper can provide useful reference for development and improvement of related materials and application of related engineering.

SUS304 stainless steel is a common stainless steel material with good corrosion resistance, heat resistance, and mechanical properties. But various defects may appear on its surface. Therefore, in response to the surface quality problems of SUS304 stainless steel plate, magnetic abrasive finishing method is used to remove the surface defects and original texture of SUS304 stainless steel plate. Traditional magnetic abrasive finishing has a relatively single magnetic field during processing, and the movement trajectory of the abrasive particles is relatively regular, so that the grinding marks are obvious. Moreover, because of overheating of the electromagnet, the working time can not be too long, which leads to lower working efficiency. Based on the traditional magnetic abrasive finishing, a pulse magnetic field has been added and a circuit has been designed. This not only complicates the magnetic field in the processing area and diversifies the processing trajectory, but also solves the serious heating problem of electromagnetic, and working efficiency of the device can be improved. Therefore, a pulsed magnetic field assisted planar magnetic abrasive finishing device was proposed, and the permanent magnet assisted with pulse magnetic field of electromagnetic was simulated using magnetic field simulation software. Firstly, the field domain was set as a transient field, and the materials in the device were set. Furthermore, an air domain was added. Finally, a calculation step was added to analyze the magnetic field under different distribution states. Based on the results of simulation, the influence of magnetic field on the motion of abrasive particles can be observed. In order to explore the influence factors of planar magnetic abrasive finishing assisted with pulse magnetic field, response surface methodology was used to optimize the data of three influencing factors: pulse current amplitude, pulse current frequency, and pulse current duty cycle. Through single factor experiments, the range of the three factors was obtained: pulse current amplitude is 15V, 25V and 35V; pulse current frequency is 1Hz, 3Hz and 5Hz; pulse current duty cycle is 15%, 50%, and 85%. By generating and adjusting the frequency and duty cycle of the pulse current through a signal generator, the pulse magnetic field generated by the electromagnet can be precisely controlled. The grinding effects of different grinding magnetic fields under different parameters on SUS304 stainless steel plate was compared through experiments. When the grinding gap is 2mm, the effects of different voltage amplitudes, current frequencies, and current duty cycles on the surface quality of the workpiece were compared. The surface quality of the workpiece before and after processing was measured and compared using a stylus surface roughness measuring instrument and an ultra depth of field 3D electron microscope, and the simulation results were verified. The experimental results of planar magnetic abrasive finishing assisted with pulse magnetic field show that through response surface data optimization, when the machining parameters are pulse current amplitude of 20V, pulse current frequency of 4.5Hz, and pulse current duty cycle of 50%, the surface roughness Ra of SUS304 stainless steel plate after grinding is reduced to 0.047μm from the original 0.346μm. The design of circuit effectively solves the serious heating problem of electromagnetic. This circuit not only effectively reduces the heat generated during working process of electromagnetic, but also ensure the stable operation of the equipment and increases the service life span of the electromagnetic. By precisely controlling the amplitude, frequency, and duty cycle of pulse current, the motion trajectory of magnetic abrasive particles can be effectively changed. The periodically changing grinding magnetic field can make the abrasive particles move periodically, achieving rolling and updating during the grinding process. This can significantly reduce the surface roughness of workpiece and provide a reliable method for improving the machining quality. This processing method has greatly improved the grinding efficiency and processing effect.

The performance of a wind power yaw braking system determines the accuracy of yaw to wind, yaw movement stability, and the safety and reliability of an entire wind turbine operation. Wind power yaw braking conditions and yaw brake pads selection affects the brake disc and brake pads braking interface wear conditions, because the brake pad material hardness is lower than that of the brake disc. Excessive wear of the caliper steel plate will cause damage to the brake disc, and result in yaw process jitter, the frequent replacement of brake pads, increased repair costs, and the decreased operational efficiency of the unit. Existing brake discs for low-speed and heavy-load applications, such as yaw and low-speed and heavy-duty braking conditions, are rarely studied, and finite element and experimental methods are typically used to measure the wear of braking interfaces. Hence, a three-dimensional simplified model of a yaw brake composed of a Q345E yaw brake disc and composite resin-based brake pad is established to address the wear problem in the yaw braking process, considering the dynamic change in the interface between the brake disc and brake pad. First, the relatively mature Archard wear theory combined with the finite element discretization calculation was adopted to accurately simulate the wear state of the yaw brake pads, and adaptive mesh technology was used to re-divide the mesh when mesh aberrations occurred. Simultaneously, the mesh in the contact area was encrypted to make the calculation results more convergent. In addition, two common shapes of yaw brake discs, namely, straight-edge type and boss-type, were selected to ensure that they had the same nominal contact area to investigate the dynamic changes and distributions of the wear depth and contact pressure of the two types of brake pads during the braking process via three influencing factors: the braking pressure, yaw speed, and friction coefficient. Finally, experimental schemes of the three factors and three levels were designed based on a full factorial simulation and Box-Behnken design response surface method. This was followed by a numerical simulation to obtain experimental results, establish the response surface model, and optimize related parameters. The results show that brake pads under different working conditions wear seriously at the friction inlet, and the wear state exhibits a significant front-end effect that is relatively serious at high contact pressures. Under the same influencing factors, the wear volume and wear depth increase with the increase of the different influencing factors. Moreover, the initial wear stage is faster due to the sudden change of the load applied, and when it reaches the stable wear stage, the contact area increases. Then, the change area becomes slower, and, in general, the straight-edge brake pad is more wear resistant than the boss-type brake pad. The brake pressure and yaw speed have a significant effect on the wear depth and contact pressure, whereas the friction coefficient is less significant for them and increases steadily over a small range. With the aim of reducing wear in practical engineering applications, optimal parameter combinations of a braking pressure of 2.001 MPa, yaw speed of 2 r/min, and friction coefficient of 0.333 were obtained via the optimization of the response surface parameters. Moreover, a simulation of the optimized working conditions was conducted. The error was less than 5%, compared with the predicted values of the response surface model, which verifies the accuracy of the response surface model. Hence, the finite element wear simulation revealed the influence of different shapes of brake pads on yaw brake wear, as well as provided technical and theoretical support for the selection of yaw brake pads.

Metal rubber (MR) is recognized for its exceptional qualities as a vibration and damping structural material, and it exhibits commendable creep resistance under regular work conditions. However, the extent of its creep resistance when subjected to environmental challenges, such as the wet marine environments found aboard ships or the oil-polluted settings that are characteristic of factory processing equipment, remains undetermined. Currently, the literature contains limited investigations into the static compressive creep behavior of MR within marine corrosive environments. This scarcity of research underscores the need for further exploration to ascertain the performance capabilities of MR under these harsh circumstances. Leveraging these insights, this study initiates the fabrication of MR specimens from 304 stainless steel wire via a series of processes including winding, drawing, blank winding, and stamping. Subsequently, the MR specimens undergo distinct surface modification treatments: silanization (S), chemical pickling (P), and a combination of chemical pickling followed by silanization (P-S). These treatments yield three categories of MR specimens that exhibit varied surface attributes. A 5wt.% NaCl solution is employed to emulate a marine environment, and an alternate immersion corrosion creep (AICC) test is conducted on the MR specimens with the aforementioned surface treatments. The post-test analysis involves the examination of the micro-morphology, elemental composition of corrosion products, corrosion resistance, and creep resistance of the three specimens. Characterization techniques, such as tungsten filament scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and electrochemical comprehensive testing are utilized to facilitate these assessments. The results show that after the AICC test, the corrosion products of the three specimens are mainly O, Fe, and Cr. The corrosion products on the surface of the untreated and S-MR specimens are covered in bulk on the surface of the wire. The P-MR and P-S-MR specimens are adhered to the metal wire in the form of a cell. The electrochemical test results show that the S-MR has the lowest corrosion potential (E_corr) and the highest corrosion current density (i_corr) under the AICC conditions, indicating that it has the worst pitting resistance and is more prone to pitting reactions. However, compared with untreated specimens, the impedance R_p and diffusion coefficient n of S-MR specimens are higher, whereas the Q value is lower, indicating that the passivation film stability is better and the corrosion rate is lower. The E_corr of P-S-MR specimens is -447.37 mV, which is relatively high, whereas their i_corr is relatively low, at 0.91 μA·cm^-2. In addition, the overall corrosion rates of S-MR, P-MR, and P-S-MR are 0.024 9, 0.019 2, and 0.013 4 mm / a, respectively, which are lower than those of the untreated specimens (0.044 1 mm / a). The results show that the silane film produced by silanization has a better protective effect on the S-MR specimens, and the comprehensive comparison shows that the P-S-MR specimens show the best corrosion resistance in the 5wt.% NaCl solution. According to the variation amplitude of the mechanical performance of each specimen during the AICC test, the creep phenomena of the four specimens occurs in different degrees in the intermediate immersion corrosion environment. The height variation amplitude h, average stiffness variation amplitude k, energy dissipation variation amplitude e, and loss factor variation amplitude l of the P-S-MR specimens are -2.23%, 19.21%, -15.14%, and -3.79%, respectively, whereas the k and e values of the untreated specimens are 29.45% and -29.31%, respectively, which are close to the failure threshold of ±30%. Moreover, the overall magnitude of the mechanical performance change amplitude maintains the same order: untreated > S-MR > P-MR > P-S-MR. These results show that the changes in mechanical performance of MR specimens are affected by the degree of corrosion. That is, the higher the degree of corrosion, the higher the degree of creep caused to the specimens. These results also indicate that the P-S treatment of MR specimens is an effective technical approach by which to improve their corrosion and creep resistance. Therefore, this research can serve as an important reference for the extension of the engineering applications of metal rubber.

The working environment of the inner surfaces of tubes in industrial production is harsh, necessitating higher performance against corrosion, friction, and wear. To improve the properties of the inner surfaces of tube and barrel parts, a high-power impulse magnetron sputtering (HiPIMS) coating method with an auxiliary anode is proposed. The auxiliary anode was first placed near the tube tail to attract plasma into the inner part of the tube. Chromium (Cr) coating was then deposited on the inner wall of a carbon steel tube with a diameter of 40 mm and a length of 120 mm. The effects of the auxiliary anode voltage on the discharge characteristics of the Cr target as well as the structure and mechanical properties of the Cr coating deposited on the tube’s inner surface were explored. The accessible depth of Cr deposition inside the tube was established. The plasma distribution inside the tube following the addition of the auxiliary anode was analyzed and a theoretical model was developed. The experiments demonstrated that the substrate current increases with higher auxiliary anode voltages, particularly at the tube tail position. When the auxiliary anode is positioned at the end of the tube, it attracts electrons deeper into the tube, resulting in increased ionization of additional ions and electrons during their movement. The ions generated by ionization are attracted to the inner wall of the tube by the negative charge carried by the tube. This can be inferred by comparing the emission spectral intensity curve between the nozzle and the tube tail. At the port position, when the auxiliary anode voltage is 20 V, the Ar+ feature peak value is the lowest, whereas the corresponding Cr* feature peak value is the highest. We infer that at 20 V, most of the energy is absorbed by the excited particles. However, under the influence of the auxiliary anode, electron escape is accelerated, inhibiting the discharge. The Cr film deposited at the tube port has a columnar structure, as shown by the cross-section morphology of the film deposited at different auxiliary anode voltages. At higher auxiliary anode voltages, the columnar crystal width decreases, and the deposited film becomes denser. As the auxiliary cathode voltage increases, the overall depth of the deposited chromium layer in the tube also increases. However, the deposition rate decreases with an increase in auxiliary anode voltage. This may be due to the higher energy of the particles that derives from the increased auxiliary anode voltage, which leads to the film densification and enhanced etching effects, thereby decreasing the deposition rate. The coating hardness and elastic modulus of the Cr film both increased initially and then decreased with increasing auxiliary anode voltage. At an auxiliary anode voltage of 40 V, the Cr coating achieved the best depth with the highest hardness and elastic modulus. Under HiPIMS discharge conditions, the effects of the auxiliary anode on the plasma can generally be summarized. First, by attracting electrons, the auxiliary anode regulates the direction of plasma’s movement. The plasma concentration can be greatly increased by the additional anode. An additional anode at the tube's end modifies the distribution of electric field lines in the vacuum chamber, reducing the number of escaping electrons. Second, high-density, high-energy plasma preferentially forms along the tube axis towards the auxiliary anode at the tube’s end, promoting further collision ionization of neutral particles inside the tube and delaying the decrease in plasma density caused by the increased distance from the target surface. The Cr coating deposited on the inner surface of the tube can be widely used in harsh environments.

Rolling bearing surface failure is a key factor that restricts the development of mechanical devices and their service life when facing the harsh working conditions of high speed and heavy load coupled with multiple factors. In a physical vapor deposition (PVD) hard coating-steel substrate system, the mechanical properties of the coating and substrate steel have differences, leading to the insufficiency of the bond strength of coating and substrate, and then, in the high-speed and heavy-duty conditions are prone to cracking, peeling, and ultimately premature failure. PVD technology can protect rolling parts under the rolling contact and reduce surface friction and wear with its high controllability, low deposition temperature, wide range of plateable substrate materials, good mechanical properties, and excellent tribological properties. Further, rolling bearings with the PVD coating can show a longer service life and higher reliability under the same operating conditions; however, there is a lack of systematic introduction on the factors affecting the bond strength and tribological properties of PVD coatings. This paper reviews the latest research results of PVD coatings and discusses effective approaches to improve the bond strength of PVD coatings from multiple perspectives, including coating structure, process conditions, deposition substrate, post-treatment of coatings, and elemental doping: (1) selecting the reasonable coating structure according to different substrates and coating materials; (2) selecting appropriate process parameters such as current, bias voltage, and temperature, according to different coating systems; (3) selecting appropriate coating types according to the mechanical characteristics of the substrate materials; (4) adopting appropriate post-treatment methods; (5) appropriately enhancing the surface roughness of the substrate; and (6) selecting appropriate elements for doping. According to the material properties of different substrates and coatings, different treatment methods are adopted to maximize the coating bond strength and extend the service life of rolling bearings. In addition, this paper introduces the excellent performance of high entropy alloy coating, providing a new solution for the surface protection of rolling bearings under harsh working conditions and effectively improves the rolling bearing surface wear and coating spalling and other failure problems. Further, it has a very large potential application prospects for rolling bearings under harsh working conditions. In addition, this paper introduces the excellent performance of high entropy alloy coating, which provides a new solution for the surface protection of rolling bearings under harsh working conditions and can effectively improve the rolling bearing surface wear, coating spalling, and other failure problems. It also has a very large potential application prospect for rolling bearings under harsh working conditions. In addition, this paper promotes the application of PVD coating in rolling bearings by employing element doping to enhance the comprehensive performance of PVD coating, and suggests the combination of PVD and post-treatment, surface pretreatment, and other methods to form “PVD with pre-treatment,” “PVD with post-processing,” and other composite surface treatment technologies. Thus, the early failure of rolling bearing surface coating caused by an insufficient bond strength and tribological properties can be solved. However, the research on a variety of PVD composite treatment technology remains lacking, and the research on its mechanism and treatment process is insufficient. In the future, if a standardized treatment process is formed, the PVD composite surface treatment technology can solve the early failure phenomenon of rolling bearing surface coatings because of the insufficient bond strength and tribological properties and promote the wider application of physical vapor deposition coatings in the field of bearings.

Integrated die-casting molds have emerged in response to lightweight, energy-saving, and environmental protection policies in the automotive industry. These molds are subjected to the alternating effects of high-temperature and high-speed aluminum liquid cooling and heating, and traditional surface treatment technologies cannot meet these harsh service conditions. The coating prepared by high-energy pulsed magnetron sputtering (HiPIMS) is dense, smooth, and exhibits good mechanical properties. The preparation of the AlCrN coating using HiPIMS technology is an important measure for improving the aluminum adhesion resistance of integrated die-casting dies. Based on plasma emission spectroscopy (OES), HiPIMS technology was used to prepare high-performance AlCrN coatings with a dense structure at various N2 / Ar flow ratios. The discharge characteristics and time-averaged OES spectra of HiPIMS were examined using a digital oscilloscope, high-voltage probe, current probe, and plasma emission monitor. The crystal phase structure, grain size, and surface cross-sectional morphology of the coating were analyzed using an X-ray diffractometer and scanning electron microscope. The nano-hardness and elastic modulus of the film were measured using a nano-indentation instrument. An anti-adhesion test with liquid aluminum was designed to assess the performance of the coating structure at 700 °C. The results showed that as the N2 / Ar flow ratios increased, the peak current under HiPIMS and peak power density also increased. The deposition rate first increased and then decreased, and the grain size and microstructure of the coating changed significantly. Numerous ionic states appeared in the film-forming environment, and the strength of CrII, AlII, and NII increased significantly. As the strength of CrII / CrI increased, the ionization rate of metal atoms in the target also increased with the N2 / Ar flow ratio during sputtering. With the change in the N2 / Ar flow rate, the coating structure primarily exhibited three states: an amorphous structure, a hcp-AlN and fcc-AlCrN mixed phase, and a single fcc-AlCrN phase. Obvious differences could be observed in the microstructure of each phase. The variation in N2 / Ar flow ratios significantly affected the structure and properties of AlCrN coatings. In the experiment, the nitrogen content of the coating remained high and demonstrated an overall increasing trend with the N2 / Ar flow ratio, ultimately approaching the stoichiometric composition in the fcc-AlCrN structure. The fcc-AlCrN phase coating with a preferred orientation of (220) was prepared at the highest N2 / Ar flow ratio, resulting in the highest hardness and elastic modulus. Simultaneously, it had the highest H / E and H3 / E2 ratios as compared with the other experimental groups. A laboratory-level efficient anti-aluminum adhesion test was next designed. In this test, the structure demonstrated good characteristics without aluminum adhesion, and the phase structure and composition of the coating did not change significantly. The surface integrity of the coating remained intact without obvious damage. The stability of the fcc-AlCrN structure in the liquid aluminum was the key to its excellent anti-aluminum adhesion performance. In this study, high-performance AlCrN coatings were prepared by varying the N2 / Ar flow ratio, which improved the aluminum adhesion resistance of the integrated die-casting die surface.

Thermal barrier coatings (TBCs) have excellent properties, including a high melting point, low thermal conductivity, and high thermal expansion coefficient, which can significantly improve the efficiency and extend the service life of high-temperature components in the aerospace industry. Due to the characteristics of the TBC preparation process, pores are inevitably present inside the coatings and significantly affect the mechanical properties of the TBCs, particularly their elastic properties. Therefore, exploring the relationship between the microstructural characteristics of TBCs and the macroscopic elasticity is crucial for optimizing the parameters of the preparation process and predicting the service life. The internal pores of TBCs exhibit complex morphologies, such as irregular shapes and rough boundaries. However, existing research on TBCs based on elliptical approximations have focused on the relationships among the porosity, size, orientation, and macroscopic elasticity without considering the effects of irregular pore morphology on the macroscopic elasticity. In this study, a water-immersion ultrasonic back-reflection experiment was conducted using test samples with an Al₂O₃ coating plasma-sprayed onto a stainless steel substrate. The experimental setup consisted of an angle meter, a 10 mm thick acrylic glass flat-bottomed reflector, and an SM-J3B-300 water-immersion ultrasonic testing system, which included a GE USIP 40 ultrasonic generator, Tektronix DPO 4034B digital oscilloscope, nominal 5-MHz water-immersion pulse-focusing probe, three-dimensional stepper device, and self-built rotational angle measurement device used for precise control of the sample’s axial rotation angle. The backscattered signal from the flat-bottomed reflector surface at the vertical incidence was used as a reference signal, and the angle meter displayed the θ_i values. The coating was continuously rotated in the x₁-x₃ plane from 0°to 90°in increments of 1°. The ultrasonic backscattered signals corresponding to different incident angles θ_i were collected as the analysis signals. A simulation was performed based on the water-immersion ultrasonic back-reflection experiment. A newly proposed random sphere model (RSM) and random void model (RVM) were separately used to build TBC simulation models based on the characteristic parameters, namely, porosity (p), aspect ratio (α), and orientation factor (λ), which were obtained from the observation and statistical analysis of multiple (>32) metallographic photos of the plasma-sprayed Al₂O₃ coating. Ultrasonic testing finite element numerical simulations with the models were then conducted to analyze the effects of different pore morphologies on the wave velocities at multiple incident angles. Combining the Christoffel equation with sensitivity analysis, which can improve the efficiency of ultrasonic signal selection, enables accurate inversion of multiple unknown elastic constants of TBCs. The effects of irregular pore morphology on the elastic constants of TBCs were revealed by comparing the elastic constants obtained through inversion from experiments and two types of models with those calculated using micromechanical theory. The results of ultrasonic measurements, numerical simulations, and theoretical calculations of the elastic constants of the plasma-sprayed Al₂O₃ coatings showed that the elastic constants exhibited obvious elastic anisotropy. Numerical simulation results based on the RSM model showed good consistency with the theoretical values, with a relative deviation of less than 3.32%. This showed that the theoretical results were more applicable to the analysis of relatively regular morphological pores that can be approximated as spheres or ellipsoids. However, the elastic constants measured based on the RVM model had a higher relative deviation of as much as 12.53%, and the relative deviation of the ultrasonic experimental results was up to 59.91%, indicating that the effects of irregular pore morphology on the macroscopic elasticity of TBCs could not be ignored. Moreover, the inversion results using the irregular RVM model were closer to the experimental results than those based on the RSM model, further illustrating that the irregular pore morphology significantly affected the elastic performance of the coating.

Numerical simulations are powerful tools for analyzing the rolling process of metal composite plates. However, the current numerical models for simulating the cold-rolling compounding of dissimilar metal-layered plates mostly adopt either interface binding or friction constraints. These approaches fail to accurately judge and simulate dynamic compounding at the interface, making it difficult to achieve precise predictions of the true stress-strain field, macroscopic warping, and thickness ratio of composite plates. Additionally, simulations involving high reduction rates in a single pass often suffer from severe mesh distortion and nonconvergence issues, hindering the integrated development of simulations in the field of rolling compounding. In this paper, we propose a novel numerical model to overcome these limitations. The finite element modeling of the Cu/Al plates in this model employs elongated meshes with an aspect ratio of at least 2. This improvement addresses the shortcomings of previous compounding criteria, which only considered normal forces, by incorporating tangential force constraints. This enhancement allows for a more accurate representation of the actual rolling compounding process, which involves the combined action of normal and tangential forces. The research objectives of this study are multifaceted. First, we aim to develop a robust numerical model that can accurately simulate the rolling compounding process of dissimilar metal-layered plates. Second, we seek to predict the quality of the composite metal plates in terms of their stress-strain field, warping degree, and post-rolling thickness ratio. The study's methodology involves several key steps. Initially, we developed a finite element model using elongated meshes with aspect ratios of at least 2. This choice of mesh design helps reduce mesh distortion and improves the convergence of the simulations. We then incorporated tangential force constraints into the model to address the limitations of previous models that only considered normal forces. This dual consideration of normal and tangential forces allows for a more realistic simulation of the rolling compounding process. The model's performance was evaluated through a series of simulations involving Cu/Al plates with various thickness ratios (2:4, 3:3, and 4:2) and reduction rates ranging from 40% to 60%. The simulation results were analyzed to assess the accuracy of the model in predicting the stress-strain field, degree of warping, and post-rolling thickness ratio of the composite plates. One of the key innovations of this model is its ability to mitigate severe mesh distortion and non-convergence issues that plague high-reduction-rate simulations. Using elongated meshes and incorporating tangential force constraints, the model provides a more realistic simulation of the rolling compounding process. This allows for more accurate predictions of the stress-strain field, warping degree, and post-rolling thickness ratio of the composite plate. The simulation results demonstrated that the proposed model can effectively simulate the rolling compounding process of Cu/Al plates with various thickness ratios and reduction rates. The predictions of the warping degree and post-rolling thickness ratio of the model were accurate, with errors within acceptable limits. Specifically, the error in predicting the degree of warping was less than 7.40%, and the error in predicting the post-rolling thickness ratio was generally less than 10%. This shows that the model can be used to predict the mass of the composite metal plates and has the potential to explore the internal mechanism of the rolling composite. In conclusion, the proposed numerical model addresses the limitations of existing models by incorporating elongated meshes and tangential force constraints. This allows for more accurate simulations of the rolling compounding process, leading to better predictions of the stress-strain field, warping degree, and post-rolling thickness ratio of the composite plate. The model initially solves serious mesh distortion and calculation non-convergence problems in high-pressure rate simulations and provides a reference for the process optimization of composite metal plates.

The adhesion and growth of organisms on engineering equipment, medical devices, and household items necessitates the efficient and safe operation of equipment and the health of the human population, which is a challenge that needs urgent solutions. Schiff base-based materials, such as Schiff bases, Schiff base metal complexes, and poly-Schiff bases, have attracted significant attention because of their unique structural features and physicochemical properties, particularly their proven antibacterial, antifungal, and antifouling activities. These materials are expected to have a wide range of applications in various fields, such as biomedicine, industry, and marine science. Schiff base compounds were first discovered approximately 160 years ago by Hugo Schiff, a German chemist, and are formed through the dehydration and condensation of aldehydes or ketones (carbonyl compounds) with amines. Methods have been developed to synthesize Schiff bases through the addition of phenols/phenol ethers or organometallic reagents to nitriles and the conversion of olefins into ketoimines. Chemical reactions of conventional Schiff bases are typically conducted in organic solvents under mild conditions and are easy to perform. However, this method requires large amounts of organic solvents, catalysts, and energy, which are prone to environmental hazards. In recent years, the green synthesis method for Schiff base materials, which can achieve efficient and precise energy use, has become a research hotspot and the main future development direction. It mainly includes ultrasound-assisted synthesis, microwave irradiation, grinding, and water-solvent methods. Schiff bases are kinetically unstable; this instability, combined with their recoverability, gives them unique inherent properties. By grafting or embedding this type of linkage into the polymer chain segments, materials can be made to share the same bonding characteristics while possessing a number of outstanding properties that are unavailable in individual structural units, particularly intrinsic self-healing, recyclability, stimulus-responsiveness, water-degradability, and eco-friendliness. Schiff base-based organics include a wide range of antimicrobial and antifouling materials that exhibit good sensitivity and inhibition of microorganisms, such as bacteria, fungi, and algae. Its main possible antimicrobial and antifouling mechanisms include the following. ①Schiff base compounds and their degradation products damage the integrity, permeability, and selectivity of the cell membrane and wall, resulting in an imbalance of osmotic pressure inside and outside the cell and intracellular metabolic disorders, leading to cell death. ②Generating reactive oxygen species (ROS) through oxidation results in the accumulation of intracellular ROS and cell death via oxidative senescence, thus inhibiting the growth and reproduction of pathogens. ③Schiff bases and their decompositions bind to essential components of microorganisms, such as proteins, enzymes, and DNA, destroying the integrity of the structure and function of the organism, thus causing antimicrobial and antifouling effects. In addition, the inhibitory and ant adhesion effects of Schiff base-based materials on bacteria and fungi are usually not explained by a single mechanism, but require a combination of multiple antimicrobial and antifouling mechanisms. Currently, Schiff base-based antimicrobial and antifouling materials fall into five main categories: Schiff bases and their metal complexes, Schiff base-based covalent organic frameworks, side-chain poly-Schiff bases, cross-linked poly-Schiff bases, and main-chain poly-Schiff bases. Schiff bases and their metal complexes are mainly small-molecule organics, which are used as biocides and antifouling agents in biomedicine and marine fouling protection and cannot be used alone as coatings or block materials. Schiff base-valent organic frameworks typically exhibit show micro-nanoparticle and lamellar structures, which are good carriers for ROS generation and can be used as functional fillers in block materials or coatings with good long-term antifouling ability. Side-chain and cross-linked poly-Schiff base materials with good biocompatibility are typically used as biomedical materials. Main-chain poly-Schiff base materials are important for marine antifouling materials because of their multifunctionality and eco-friendliness. This review paper briefly describes the history, chemical characteristics, and synthetic methods of Schiff base-based materials, with emphasis on their research progress and application prospects in antibacterial and antifouling materials. Common scientific issues in related research are highlighted, and future directions for the development of Schiff base-based antimicrobial and antifouling materials are proposed. This review is a reference for researchers and professionals in chemistry, materials, and marine antifouling.

Metal equipment is vulnerable to corrosion when used in harsh marine environments. The speed, fuel consumption, and service life of marine equipment are greatly reduced owing to seawater corrosion, which results in significant economic losses every year, severely impeding the development of the national economy. Therefore, protecting marine equipment from corrosion damage has always been an urgent issue. Currently, coating technology is one of the most effective and commonly used methods for protecting metals from corrosion. Preparing self-healing coatings with better performance by adding micromaterials and nanomaterials to the coatings and further improving the corrosion protection ability of the coatings has recently become an important research direction for metal protective coatings. However, most inorganic microcarriers and nanocarriers have agglomeration problems in organic coatings, which affects the corrosion resistance and service life of self-healing coatings. In this study, the natural halloysite microtube (HMT) was reamed by alkali etching to increase its inner diameter. Secondly, the corrosion inhibitor, 2-mercaptobenzothiazole (MBT), was loaded into alkali-etched halloysite microtubes (HMTs) by vacuum adsorption in a vacuum chamber. Then, chitosan (CS) was coated on the outer surface of HMTs under acidic conditions to prepare micron fillers with a corrosion inhibition function. Finally, micron fillers were added to the PDMS coating at the rate of 15 wt.% and fully stirred to prepare the self-healing coating. Fourier-transform infrared spectroscopy (FTIR) was used to confirm the successful loading of MBT into HMTs, and the corrosion inhibition function of the inhibitor remained effective. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to observe the morphological structures of HMTs, HMTs-MBT, and CS-HMTs-MBT. Through thermal gravimetric analysis (TGA), HMTs were shown to carry approximately 13 wt.% of MBT, and HMTs encapsulated with CS accounted for approximately 61 wt.% by mass. The dispersion of various samples in polydimethylsiloxane (PDMS) coatings was tested, demonstrating that CS encapsulation could enhance the dispersion of microcarriers within the coating. Electrochemical impedance spectroscopy (EIS) was used to assess the self-healing ability of the coating. An analysis of |Z|_{0.01 Hz} indicated that the self-healing ability of the coating reached its maximum on the fourth day. Data from impedance measurements were fitted using ZSimpWin to validate the corrosion resistance of the self-healing coating. After a four-day immersion experiment, energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were utilized to confirm that the copper ion content at the scratch site of the self-healing coating had dropped to zero. In addition, scanning Kelvin probe (SKP) tests indicated the disappearance of the potential well at the scratch site, signifying that the coating had been repaired by the corrosion inhibitor. Utilizing the excellent dispersion properties of CS in organic coatings enhances the dispersibility of CS-HMTs-MBT in PDMS coatings. When the coating was scratched, the corrosion inhibitor MBT was released and adsorbed onto the metal surface, forming a tight film that isolates corrosive substances. This study performed etching modification on halloysite micron tubes to increase their corrosion inhibitor loading capacity and verified the feasibility of carrying corrosion inhibitor MBT in the modified tubes. On this basis, CS film was applied to the micron tubes to improve the dispersion of the micron tubes in the coating. The self-healing coating was prepared by loading the corrosion inhibitor and encapsulated with chitosan as a filler in the inner cavity of the HMTs. Controlled and long-term release, protecting metal parts and compensating for performance deficiencies of ordinary coatings, was achieved. This study thus demonstrates the possibility of preparing self-healing coatings suitable for harsh corrosive environments.

Titanium dioxide nanotubes (Titanium dioxide nanotubes, TiO₂ NTs) have garnered significant attention in recent years owing to their unique nanostructures, high specific surface areas, and exceptional antibacterial and drug-release capabilities. As innovative surface-modification materials, TiO₂ NTs show great promise for use in biomedical applications, particularly in infection control and drug delivery. The remarkable properties of TiO₂ NTs, including their abilities to interact with biological systems, have made them a focal point of research for the development of new therapeutic strategies, particularly for combating bacterial infections. This review systematically examines the fabrication methods of TiO₂ NTs and their applications in the antibacterial field, focusing on their roles in controlling bacterial infections and regulating drug release mechanisms. The methods used to fabricate TiO₂ NTs, such as anodization, sol-gel processes, and hydrothermal synthesis, are critical for controlling their size, morphology, and surface properties, all of which directly influence their performance in various biomedical applications. These fabrication techniques allow for precise control over nanotube structures, which optimizes their drug-loading capacity and ensures their effectiveness in both infection prevention and controlled drug release. Moreover, TiO₂ NTs are highly effective at preventing bacterial adhesion and biofilm formation, which are key challenges in medical treatments. Further, TiO₂ NTs can be functionalized by loading various antibacterial agents, such as antibiotics, silver nanoparticles, and other bioactive compounds, to enhance their therapeutic effects. This review discusses various loading techniques, including physical adsorption, layer-by-layer self-assembly, and solution impregnation, for improving the efficiency of drug delivery. Physical adsorption is a simple and widely used technique for loading antibacterial agents, where the agents are adsorbed onto the surfaces of nanotubes. In contrast, layer-by-layer self-assembly creates a more complex structure with multiple layers, thus allowing for a more controlled and sustained release of drugs. Solution impregnation, which is another important technique, facilitates the incorporation of therapeutic agents into nanotubes and ensures that the drugs are released gradually, thus enhancing their antibacterial effects over an extended period. Additionally, sealing technologies are crucial for enhancing the drug release efficiency. Sealing methods typically involve the use of polymers or composite materials that encapsulate drugs, which prevents their premature release and ensures a more controlled and sustained-release profile. These sealing technologies improve the stability and performance of TiO₂ NTs in biological environments and thereby optimize their therapeutic benefits. Despite the promising antibacterial properties and biocompatibility of TiO₂ NTs, their practical applications face several challenges. Issues such as the structural stability of TiO₂ NTs in biological environments, precision of drug release, and long-term safety must be addressed. The degradation and morphological changes in TiO₂ NTs in biological fluids can compromise their functionality and biocompatibility. Moreover, ensuring precise drug release is challenging because the careful design of the nanotube structure and loading methods are required. Long-term safety, particularly the potential toxicity of TiO₂ NTs and their degradation products, must be further evaluated to ensure their safe use in medical applications. Future research should focus on optimizing the design of TiO₂ NTs by exploring new fabrication techniques and developing multifunctional composite materials that combine TiO₂ NTs with other materials, such as polymers, natural biomolecules, or nanoparticles. These composite materials can enhance the stability and drug loading as well as control the release of TiO₂ NTs, which thereby expands their applications in a variety of therapeutic contexts. Furthermore, clinical trials are required to validate the long-term safety and efficacy of TiO₂ NTs in real-world medical applications. By addressing these challenges and advancing the development of TiO₂ NTs, their potential for widespread use in the medical field can be realized to thereby provide innovative solutions for infection prevention, controlled drug delivery, and other biomedical treatments.

Al-Si alloys are ideal materials for the preparation of aluminum alloy engines. However, the wear resistance of Al-Si alloys produced through casting technology is poor, making them unsuitable for use under harsh working conditions inside an engine. They can only be used to make external cylinder blocks. Coatings prepared by supersonic plasma spraying have advantages such as high bonding strength and a dense microstructure. Therefore, using supersonic plasma spraying technology to prepare structurally excellent Al-Si coatings on the surface of Al-Si alloys can improve their high-temperature friction performance, which is expected to facilitate the preparation of all-aluminum engines. In this study, Al-35Si-4Fe powder was used as the raw material, and ultrasonic plasma spraying was used to prepare an Al-Si alloy. Owing to the high heat input in the ultrasonic plasma spraying process, Al is burned out, thus achieving the in-situ preparation of Al-40Si-5Fe coatings. According to the differential scanning calorimetry analysis results of the Al-40Si-5Fe coating, heat treatment of the Al-40Si-5Fe coating was carried out at 330 ℃, which promoted the transformation of the coating structure and ultimately improved the high-temperature friction performance of the coating. The microstructures of the coatings before and after the heat treatment were observed using scanning electron microscopy and transmission electron microscopy. The results indicated that the spray coating structure was dense and presented a typical thermal spray coating structure. Owing to the difference in cooling rate, there was a significant difference in the upper and lower microstructure of a single spread. The upper part of a single spread consisted of a primary Si phase and an Al/Si eutectic phase, while the lower part consisted of an incomplete amorphous structure. The average size of the primary Si phase in the sprayed coating is approximately 200 nm. During the 330 ℃ heat treatment process, thermal activation energy promoted the fusion and growth of the Si phase. The formation of a mesh-like Si-phase skeleton with a smooth surface inside the coating significantly improved the uniformity of the coating structure. The hardness and elastic modulus of the sprayed coating are 460.4 HV0.2 and 98.6 GPa. After heat treatment, owing to grain growth and amorphization, the hardness of the coating gradually decreased, and the elastic modulus gradually increased. The hardness and elastic modulus of the 330 ℃×24 h heat-treated coating are 336.3 HV_0.2 and 108.5 GPa, respectively. Under the dry friction test conditions of load 3 N, stroke 4 mm, and frequency 5 Hz at 220 ℃, the average coefficient of friction and wear rate of the 330 ℃×24 h heat-treated coating were 0.38 and 1.35×10^-4 mm³/Nm, respectively, which are 19.1% and 5.6% lower than those of the sprayed coating, respectively. Using a scanning electron microscope to observe the worn surface of the coating, it was found that there were obvious furrows, plastic deformation, and adhesive damage on the worn surface of the sprayed coating. Therefore, the wear mechanisms of the sprayed coatings are abrasive and adhesive. A large number of furrows were also found on the surface of the 330 ℃×24 h heat-treated coating, but the degree of plastic deformation was low and adhesion damage was less. Therefore, the wear mechanism of the 330 ℃×24 h heat-treated coating is mainly abrasive wear, accompanied by a small amount of adhesive wear. The network Si phase structure in the 330 ℃×24 h heat-treated coating can maintain the strengthening effect on the substrate in an environment of 220 ℃, effectively reducing the degree of plastic deformation of the coating and the adhesion behavior between friction pairs during the friction process, and significantly improving the high temperature friction performance of the coating.

Due to long-term service, the stainless steel cladding on the bottom and wall of a spent fuel pool in a nuclear power plant can cause cracks, holes, and other defects, leading to the leakage of radioactive liquid and negatively affecting the environment. This in turn affects the safe operation of the plant. Traditional manual welding by divers or shutdown maintenance of nuclear power plants cannot meet current maintenance requirements, and local dry automatic underwater welding maintenance is a development trend. Compared with the underwater welding of the bottom cover plate, the pressure difference in the wall position due to drainage and the effects of gravity on the molten pool are more obvious. The welding and drainage process for underwater repair of the wall cover plate is more difficult to implement, significantly increasing repair difficulties. Therefore, this study explores and optimizes the local dry drainage and welding process of a wall cladding. To simulate the underwater repair of a spent fuel pool wall cladding in a nuclear power plant, a local dry underwater tungsten inert gas (TIG) shielded welding repair system was developed that includes a mobile positioning mechanism, TIG power supply, underwater TIG welding drainage device, control system, wire feeder, and experimental pool. The local dry underwater TIG welding drainage device has high adaptability in multiple positions and is suitable for welding repair in underwater environments at wall positions. The study employed a self-built underwater TIG wire filling welding test system and used a square repair plate of 80 mm × 80 mm × 4 mm to address the large area of cracks and hole defects in the weld seam of the spent fuel pool wall cladding. After the repair plate was aligned with the original weld seam of the spent fuel pool wall cladding to be repaired, the welding of the repair plate was decomposed into horizontal and vertical positions for welding. A KEMPPI TIG welding machine and Funis KD7000 wire feeder were used as experimental equipment to conduct TIG wire filling welding process tests in both horizontal and vertical positions in underwater and air environments. The microstructure, chemical composition, and phase composition of welded joints were compared under the two environments. The results show that due to rapid cooling of the molten pool, the cross-sectional size of the underwater environment weld is slightly smaller than that of the air environment. The content of δ ferrit and hardness in the underwater environment is higher than that in the air environment, and the maximum microhardness appears at the aggregation of feathery ferrite. The grain size of the weld seam in the underwater environment is slightly larger than that in the air environment, whereas the corrosion resistance is slightly lower than that in the air environment. However, the difference is not significant. The Cr element is precipitated from the weld seam metal in both environments to improve its corrosion resistance. The quality of the welding repair of the underwater repair plate is essentially comparable to that in the air environment and meets the repair requirements for the wall position of the spent fuel pool cladding plate. The proposed dry underwater TIG shielded welding repair system can be used in the protection and repair of 304 stainless steel claddings in underwater environments. This study presents the following innovations. Defect free stainless steel clad plate repair welds were prepared at the wall position of an underwater environment using the local dry underwater TIG wire filling welding process. A comparative analysis was conducted to assess the effects of the underwater environment on the microstructural evolution, phase composition, and chemical elements of the transverse and vertical positions of the cladding weld seam. The microhardness and corrosion resistance of the stainless steel clad plate weld prepared in the underwater environment are found to be similar to those of the stainless steel clad plate weld prepared in the air environment.

In recent years, ultra-high-strength steel (UHSS) has been widely utilized in engineering structures, mining machinery, and military equipment. However, the high strengthening of UHSS poses two significant challenges to welding technology. On one hand, it leads to higher peak residual stresses induced by the welding process, which can cause hot cracks, cold cracks, stress corrosion, and fatigue failure. On the other hand, significant welding deformation is inevitably generated when thin-plate UHSS structures are welded. Welding deformation not only affects the appearance quality and dimensional accuracy of the product but also brings difficulties in welding assembly. Currently, research on residual stress and welding deformation by scholars remains very limited. Recent achievements in computational welding mechanics have demonstrated that numerical simulation technology based on the finite element method is a promising approach to determine the residual stresses in welded joints or even large welded structures. This study focuses on 1600 MPa grade UHSS, used for a specific type of vehicle. Tensile tests at room temperature, 200, 400, 600, and 800°C were conducted on a universal tensile testing machine to obtain stress-strain curves under different temperature conditions, and to determine the yield strength of UHSS at each temperature from the curves. The thermal expansion specimen was heated to 1000°C and then cooled to room temperature to obtain the strain-temperature curve and phase transition temperature of UHSS during heating and cooling processes. JMatPro software was used to obtain other thermophysical parameters of UHSS, and to establish a material model and phase transformation model for UHSS. Subsequently, a finite element calculation method was developed using SYSWELD software, which considers the solid-state phase transformation of UHSS and combines multiple fields of thermal metallurgy mechanics. In the numerical simulation, the microstructure calculations of martensite and austenite were considered for the UHSS. During the heating process above the starting temperature of the austenite transformation, martensite begins to transform into austenite. When the temperature reaches the end temperature of the austenite transformation, the austenitization of UHSS is completed; during the cooling process, the undercooled austenite in the heat-affected zone transforms into martensite. The double-ellipsoidal heat source model proposed by Goldak was used as the welding heat source model. In addition to considering material nonlinearity, geometric nonlinearity was also considered in the numerical simulation. The developed numerical simulation method was used to simulate the residual stress and welding deformation of UHSS T-joints under the free state and different restraint positions. In the restrained cases, the calculation of the residual stress and welding deformation was completed in the constrained state. When the joints cooled to room temperature, the structural restraint was released, and a free restraint was used to fully release the residual stress and welding deformation of the T-joint. Finally, the residual stress and welding deformation results for the UHSS T-joints at different structural restraint positions were obtained. Based on the numerical simulation results, the influence of the structural restraints and their positions on the residual stress and welding deformation has been discussed. The numerical simulation results show that structural restraints increase the peak longitudinal tensile and compressive stresses of T-joints and reduce the peak transverse tensile stress, as well as compressive plastic strain, lateral shrinkage, and angular deformation. This effect is more significant when the restraint position is closer to the weld seam. To ensure the safety of welding structures, when applying the structural restraint method in actual welding, the position of the structural restraint should not be too close to the weld seam. The numerical simulation of the study of restraint and restraint positions provides a theoretical basis for controlling the residual stress and welding deformation in UHSS.