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.

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.

Continuous-fiber-reinforced resin-based composite materials represent a novel class of high-performance composites that have gained traction in recent years. The use of additive manufacturing technology for fabricating these composite materials offers significant advantages, including enhanced manufacturing flexibility and high forming efficiency, thereby making it a key research focus. Herein, the characteristics of both resin matrix and fiber materials are summarized, followed by an examination of the extrusion and impregnation processes involved in the additive manufacturing of continuous fiber-reinforced resin-based composites. Furthermore, the impact of process parameters such as temperature, printing speed, and printing spacing on the material are discussed. Additionally, the microstructure at the fiber-matrix interface and between layers are discussed, in addition to the mechanical properties of the material, including tensile and bending strengths. Finally, the challenges associated with increasing demand and performance limitations in the additive manufacturing of these composites are highlighted, proposing recommendations for their development, such as enhancing material recyclability and optimizing the additive manufacturing process. Both thermoplastic and thermosetting resins typically serve as matrix materials. Thermoplastic materials, exhibiting relatively low melting temperatures, facilitate processing in additive manufacturing. However, the high viscosity of these materials contributes to the low impregnation between fibers and resin, resulting in relatively lower mechanical properties than those of continuous fiber-reinforced composite materials produced via conventional methods. Conversely, thermosetting materials exhibit low viscosity, thereby enhancing fiber impregnation. However, they present challenges in the formation of composite materials, thereby increasing production costs. Additionally, additive manufacturing of thermosetting composite materials generates waste, contributing to material loss. Therefore, investigating the recyclability of these materials remains a crucial area for future research. The additive manufacturing process for continuous fiber-reinforced composite materials is influenced by factors such as fiber impregnation, material extrusion, fiber volume fraction, fiber orientation, and processing temperature, all of which influence material formation. However, significant challenges persist in additive manufacturing, and further improvements in the manufacturing process are essential. Research indicates that compared with composite materials produced via conventional processes, those fabricated via additive manufacturing exhibit lower mechanical properties. The primary factors influencing the mechanical properties of the final material include the bonding between the fiber-matrix interfaces as well as between layers. Inadequate bonding between the materials results in pore formation, causing stress concentration within the material and reducing its mechanical properties, thereby accelerating material failure. To further enhance the performance of fiber-reinforced composite materials and address existing limitations, future research must prioritize the following aspects. First, different matrix materials exhibit distinct effects on the performance of composite materials. Selecting an appropriate matrix material is crucial, necessitating further research into novel resin matrix materials. Additionally, as the use of composite materials increases, their recyclability has become as a critical constraint for industrial applications. Therefore, future research on material recyclability must be prioritized. Second, in the context of additive manufacturing of composite materials, in addition to the inherent properties of the materials, multiple avenues for process improvement exist. The impregnation process can be optimized via auxiliary techniques, such as plasma and oxidation treatments. Furthermore, controlling process parameters such as printing speed, temperature, and environmental conditions is essential for ensuring consistent material properties. Further investigation into the influence of these parameters on the material properties is necessary. Third, defects such as low interface performance and porosity in composite materials are typically attributed to insufficient compaction during the manufacturing process. Improving the compaction process or performing post-processing on the material can significantly enhance the performance of additive manufacturing.

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.

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.

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.

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.

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.

The precise modulation of adhesion properties on superhydrophobic surfaces is recognized as a critical pathway for advancing functional surface engineering, with extensive applications in mechanical, aerospace, and biomedical engineering. In this context, the adhesion behavior of water droplets interacting with engineered surfaces is systematically summarized, with particular emphasis on the influence of surface microstructures, chemical compositions, and external stimulation on the adhesion of superhydrophobic surfaces. By drawing inspiration from natural superhydrophobic biological systems, such as lotus leaves, rose petals, and butterfly wings, which exhibit tailored adhesion properties, the fundamental mechanisms underlying solid-liquid adhesion behavior are elucidated, and advanced strategies for its modulation are developed. Currently, advanced characterization techniques have been standardized to quantify adhesion forces and validate modulatory mechanisms between solid and liquid. Contact angle (CA) measuring instrument systems are utilized to measure the minimum angle at which a water droplet begins to slide on an inclined surface, with a high-speed camera capturing dynamic water droplet behaviors during sliding. Adhesion measuring instruments coupled with a high-speed camera enable the nanoscale mapping of adhesion forces under controlled water droplet volume and speed of motion of the carrier table conditions. In addition, computational fluid dynamics (CFD) simulations are employed to model the solid-liquid interactions, providing insights into the mechanisms affecting adhesion on the superhydrophobic surfaces. The adhesion behavior between solid and liquid is primarily governed by the surface microstructures and chemical composition. The surface microstructures with different shapes are fabricated through laser irradiation, template replication, or lithography technologies. For instance, microstructures with various geometries are fabricated through precise adjustments of laser processing parameters, such as energy density, scanning pitch, and scanning speed, to enhance air entrapment and minimize solid-liquid contact areas. Concurrently, densely arranged micropillar arrays or porous networks are designed to change the solid-liquid contact state, enabling controlled water droplet pinning or directional transport. In addition, the transformation between low-adhesion superhydrophobic surfaces and high-adhesion superhydrophobic surfaces is further modulated by changing the chemical composition of the surface. Self-assembled monolayers (SAMs) terminated with fluorinated groups or silane derivatives are uniformly applied to reduce the surface energy, integrating stimuli-responsive polymers, such as pH-sensitive polyelectrolytes or thermoresponsive poly(N-isopropylacrylamide) (PNIPAM), to enable dynamic adhesion transitions. A synergistic combination of structural patterning and chemical modification is demonstrated to generate adhesion patterns for programmable water droplet manipulation, as exemplified by spatially selective plasma etching followed by region-specific silanization. Furthermore, external stimulation, including light irradiation, magnetic fields, and temperature variations, is employed to achieve reversible and real-time modulation of adhesion on the superhydrophobic surfaces. Photoresponsive surfaces embedded with azobenzene derivatives or titanium dioxide (TiO₂) nanoparticles are engineered to undergo light-triggered adhesion transforms. Under ultraviolet (UV) illumination, azobenzene-modified surfaces exhibit cis-trans isomerization, which alters the adhesion properties, whereas TiO₂-coated surfaces leverage photocatalytic decomposition to remove hydrophobic layers, enabling dynamic switching between low and high adhesion states. Similarly, thermoresponsive coatings are designed to undergo hydrophilic and hydrophobic transitions above specific critical temperatures, thereby facilitating temperature-dependent adhesion control. Magnetic field-responsive superhydrophobic surfaces are constructed by embedding ferrofluids or paramagnetic particles into superhydrophobic matrices, which allows noncontact water droplet manipulation through external magnetic gradients. The method of modulating surface adhesion through electric fields has been developed to modulate the solid-liquid contact state via applied voltages, achieving precise solid-liquid adhesion transformation. Practical implementation of tunable adhesion superhydrophobic surfaces is demonstrated across diverse domains. In microfluidic systems, programmable adhesion gradients have been engineered to guide water droplet routing for high-throughput bioassays, whereas ice-phobic superhydrophobic surfaces with tunable adhesion have been developed to mitigate ice accretion on aerospace components. Self-cleaning technologies exploit low-adhesion superhydrophobic surfaces to achieve contaminant removal by sliding water droplets, whereas high-adhesion superhydrophobic surfaces are tailored for targeted drug delivery, thereby enabling the non-destructive release of site-specific therapeutic agents. This review emphasizes the importance of research on the mechanisms and methodologies of adhesion modulation on superhydrophobic surfaces. By addressing the existing challenges and integrating emerging technologies, the development of tunable adhesion superhydrophobic surfaces exhibits excellent prospects for advancing developments across various scientific and engineering disciplines.

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.

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.

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.

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.

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.

Single-crystal diamond (SCD), owing to its exceptional physical properties—including an ultrawide bandgap of 5.5 eV, an extremely high breakdown electric field of 9.9 MV / cm, and an outstanding thermal conductivity of 22 W / (cm·K)—is widely recognized as a revolutionary material capable of overcoming the performance limitations of silicon-based integrated circuits (ICs). However, the extraordinary hardness (Mohs hardness of 10) and extreme chemical inertness of diamonds present significant challenges for achieving atomic-level surface polishing, which is crucial for their application in high-end chip manufacturing. This study focuses on the development of atomic-level polishing techniques for SCD, systematically reviews the evolution of polishing technologies from micro / nanoscale to atomic precision, and identifies key breakthroughs to overcome existing machining limitations. Additionally, this study examines the characteristics and applicability of various polishing methods, thus providing valuable insights for practical implementation. First a mechanical polishing techniques, including conventional and ultrasonic-assisted methods, are investigated comprehensively. Whereas these approaches offer straightforward processes, the inherent “hard-on-hard” friction inevitably introduces surface defects, thus rendering it difficult to achieve subnanometer surface smoothness. Subsequently, high-energy beam polishing technologies, such as lasers, ion beams, and plasma polishing, are examined. Although these methods replace abrasive particles with high-energy particles, issues such as inferior selectivity, deep thermally affected zones, and particle implantation limit their ability to achieve low subsurface damage and subnanometer planarization. The third category, i.e., multifield coupled polishing, which includes chemical-mechanical polishing and plasma-assisted polishing, leverages synergistic effects for surface planarization. However, these methods are characterized by complex processes and low polishing rates. Based on a detailed comparative analysis, this study highlights the significant challenges in satisfying the stringent requirements of IC manufacturing: subnanometer precision, minimal damage, and high processing rates. The findings suggest that, although existing polishing techniques are adopted in specific applications, they remain inadequate for completely satisfying the abovementioned demanding criteria. Achieving atomic-level surface polishing requires not only gradual process improvements but also systematic innovations in theoretical understanding and process development. This study emphasizes the necessity of cross-scale control from macroscopic process parameters to microscopic atomic behavior to precisely regulate material removal mechanisms, including the synergy between mechanical shear and chemical etching, as well as the energy threshold for atomic bond breaking. At the fundamental research level, the development of atomic-resolution in-situ characterization techniques and first-principles computational models is crucial for establishing quantitative relationships between process parameters and atomic surface configurations. The results indicate that atomic-scale manufacturing must rely on multifield synergistic regulation combined with in-situ atomic-level monitoring and intelligent control to achieve precise process optimization and further advance ultraprecision manufacturing. Despite significant progress, several technical bottlenecks remain in achieving atomic-level polishing for SCD. First, multifield coupling mechanisms are yet to be fully understood, thus resulting in trade-offs between the material-removal rate and surface quality in mechanical polishing, as well as issues such as high equipment costs and instability in energy-beam polishing. Additionally, multifield coupling techniques present challenges such as dynamic parameter mismatches (e.g., pH fluctuations and uneven light distributions), thus hindering stable and efficient processing. Second, intelligent control systems for polishing processes remain underdeveloped, with limited real-time optimization capabilities and insufficient integration of smart algorithms with in-situ characterization techniques. This results in a trial-and-error approach for process optimization. Third, the industrialization of green and efficient processes is hampered by key obstacles such as high energy consumption, environmental risks, and low process repeatability, which pose significant constraints for large-scale applications. Hence, future research should focus on three key directions: (1) deepening the understanding of multifield coupling mechanisms, including the interactions between mechanical forces, chemical etching, and energy fields (e.g., light, sound, and plasma), and establishing quantitative models of parameter synergy; (2) advancing intelligent control technologies, such as machine learning-based algorithms for real-time process optimization, and developing high-precision multifield coupling equipment to enhance process stability and consistency; and (3) promoting green and efficient processes, including the development of environmentally friendly chemical systems and energy-saving machining methods, as well as establishing standardized protocols for industrial implementation. The key innovation of this study is its systematic evaluation of polishing technologies and the identification of critical research directions to overcome diamond-machining challenges. By comprehensively assessing the strengths and limitations of existing methods, this study provides a solid foundation for the development of next-generation diamond-based ICs as well as offers valuable insights for academic researchers and industry professionals in advanced semiconductor manufacturing.

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.

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.

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.

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.

The rapid development of flexible electronics, microelectromechanical systems (MEMS), and integrated circuits has led to a pressing demand for surface microfabrication of materials. Existing chemical wet processes or low-pressure plasma processing technologies have been widely used for surface microfabrication; however, these microfabrication technologies have certain shortcomings, such as complex processes, high processing costs, low energy efficiency, and environmental unfriendliness. To achieve patterned surface microfabrication, traditional microfabrication methods require the use of masks or photolithography processes which limit the efficiency and application scope of the microfabrication method. Therefore, there is an urgent need to explore new surface microfabrication methods that are low-cost, green, maskless, versatile, and noncontact. An atmospheric-pressure cold plasma jet is a plasma plume formed using the action of airflow and an electric field to produce plasma in the discharge region and eject it from an orifice at a low gas temperature. Atmospheric-pressure cold plasma jet microfabrication technology is found to be advantageous because it is environment-friendly, low-cost, low-temperature, strongly reactive and pure dry method having no mechanical contacts. Atmospheric-pressure cold plasma jets have been widely used in localized surface modification, maskless surface etching, and direct deposition of functional thin films. However, microfabrication still faces challenges in terms of plasma jet stability, processing accuracy, and collaborative processing. Therefore, it is extremely essential to explore the research progress, existing problems, and future development trends in the generation mode, surface microfabrication methods, and processes related to atmospheric-pressure cold plasma jets. Firstly, the generation modes and commonly used electrode structures of atmospheric-pressure cold plasma jets were summarized and analyzed. By comparing the characteristics of four common discharge modes, namely, corona discharge, dielectric barrier discharge, arc discharge, and spark discharge, the commonly used discharge mode that generates an atmospheric-pressure plasma jet was demonstrated. Furthermore, the characteristics and applicable scenarios of single-needle, ring, needle-ring, and plate-plate type electrode structures were analyzed. Then, the research scenario of surface microfabrication technology of atmospheric-pressure cold plasma jets on surface modification, material etching, and film deposition was elaborated. Plasma jet surface modification is a general “equal material processing” method. According to the different modified surfaces, the application of plasma jets in material modification research can be roughly divided into three aspects: modifying the substrate to meet specific requirements, modifying the functional layers of devices to achieve specific functional requirements, and as an auxiliary processing method, providing assistance for other surface microfabrication methods. Herein, a systematic summary and analysis of the three surface modifications are presented. Atmospheric-pressure cold plasma jet etching, as a “subtractive processing” method, can etch substrates and also selectively etch some functional layer materials. In addition, the etching mechanism of an atmospheric-pressure cold plasma jet is summarized and discussed. As an “additive processing” method, a comprehensive review of atmospheric-pressure cold plasma jet surface deposition is also presented. This method can deposit various types of thin films or coatings with different properties, such as organic polymer, inorganic and conductive metal thin films. Finally, the main challenges that exist in plasma jet surface microfabrication technology are discussed, and its future development direction is highlighted. This review can be used as a basis for more in-depth research on methods and technologies for the surface microfabrication of atmospheric-pressure cold plasma jets and to improve the application level of atmospheric-pressure cold plasma jets in advanced manufacturing fields such as flexible electronics, MEMS, and integrated circuits.

Atmospheric plasma spraying (APS) is one of the most extensively sprayed techniques,which can provide protective coatings that enhance the durability and performance of components from various industries, including manufacturing, aerospace, and power generation. This technology has gained prominence due to its versatility, high deposition rate, and cost-effectiveness, making it suitable for large-scale industrial applications. The APS can form a plasma jet through an electric arc between the cathode and the anode. The primary gases, typically are argon or nitrogen, and the secondary gases, such as hydrogen or helium, are ionized to create a high-temperature plasma plume. When the APS process beginning, the coating material, typically in powder form, is injected into the plasma jet. Here, the particles are subjected to intense heat, which causes them to melt or partially melt while simultaneously accelerating toward the substrate. Upon impact with the prepared substrate surface, the molten particles flatten and rapidly solidify, forming the coating. In this paper, the three sequentially interlocked phases of the APS process is presented: plasma jets, flying particles, and coating deposition. Research related to the characteristic properties of each phase and its evolution laws has been conducted by integrating experimental monitoring and numerical simulations. The generation of the plasma jet marks the beginning of the APS process. The plasma jet, formed by the ionization of gases, is characterized by extremely high temperatures. The temperature, velocity, and stability of the jet are predominantly influenced by the arc energy within the torch and the plasma ionization energy. These parameters are critical because they determine the thermal and kinetic energies imparted to powder particles. A stable and high-energy plasma jet ensures that the particles are adequately heated and accelerated, setting the basis for subsequent stages of the spraying process. As the plasma jet propels the powder particles forward, they transition to the flying-particle. During this phase, the particles are heated and accelerated by the jet. The temperature and velocity of these particles play pivotal roles in determining the coating quality. Higher particle temperatures and velocities enhance the ability of the particles to melt and flatten upon impact with the substrate, leading to improved coating density and bond strength. The physical properties of particles, such as their size and shape, also influence their interaction with the plasma jet. Research has demonstrated that particles with higher velocities are more effective at filling the gaps in coatings, contributing to a more uniform and dense coating. The interaction time between the particles and the jet is another critical factor; sufficient time is necessary for the particles to absorb adequate heat and reach the desired velocity. The final stage of the APS process is coating deposition, which involves the impact of molten particles on the substrate. The spread of these particles and their interactions with the substrate and the underlying layers are critical for the morphology, composition, and overall quality of the coating. The state of molten droplets at the time of impact, including their temperature and viscosity, determines how they spread and solidify. The kinetic energy of the particles upon impact also influences the degree of flattening and the resulting bond strength with the substrate. The nature of the contact between the molten droplets and the substrate, including factors such as surface roughness and cleanliness, affects adhesion and final coating properties. The study of atmospheric plasma spraying processes offers a profound understanding of the interplay between various parameters and the resulting coating characteristics. It is invaluable for optimizing the spraying process, ensuring consistent coating quality, and expanding the applications of APS in various industries. However, it still has challenges in current research. A significant challenge is to eliminate the jet fluctuations, which can affect the stability and uniformity of the coatings. Thus, the further research is required to develop more stable plasma jets and mitigate the adverse effects of these fluctuations. Additionally, the study of multiparticle stacking and lapping remains an area requiring further exploration. Moreover, understanding the complex interactions between multiple particles during deposition can lead to better control of the coating microstructure and improved its performance. Future research should focus on advanced diagnostic techniques and numerical simulations to unravel these complexities and lay a basis for more sophisticated and efficient APS technology.

Nanosecond laser direct writing (NDLW) is an advanced surface processing technique that utilizes high-energy nanosecond pulsed lasers to induce localized modifications on metallic materials. Due to its ability to precisely control surface morphology through mechanisms such as laser ablation, photothermal, and photochemical reactions, NDLW has been widely adopted in the fabrication of microscale surface structures. When applied to polished metal substrates, NDLW typically results in a highly (super)hydrophilic surface due to the formation of oxides and increased surface roughness. However, these laser-induced surfaces can undergo further wettability transformation toward (super)hydrophobicity through post-treatment strategies that are environmentally friendly and free of chemical modifiers. In recent years, there has been growing interest in developing green, sustainable methods to regulate surface wettability, especially for applications in aerospace, biomedical engineering, and energy systems. These applications demand robust, durable, and multifunctional surface properties, including anti-icing, self-cleaning, antibacterial, and drag-reduction functionalities. Unlike traditional chemical modification methods that involve hazardous fluorinated compounds or silanes, emerging approaches focus on physically driven processes such as air exposure, thermal annealing, and secondary laser treatments to modify surface chemistry and energy without introducing environmental burdens. This paper provides a comprehensive overview of the theoretical basis of wettability, including classical models such as the Young, Wenzel, and Cassie-Baxter models, and elaborates on the role of surface roughness and surface energy in determining hydrophobic or hydrophilic behavior. Special attention is given to the mechanisms by which nanosecond laser processing induces micro / nano-hierarchical structures and alters surface states on metals such as titanium, aluminum, stainless steel, and copper. Subsequent to NDLW, environmental exposure often results in gradual absorption of low-surface-energy organic compounds from ambient air. This spontaneous aging process, albeit slow (often taking weeks), transforms laser-textured metal surfaces into superhydrophobic states, as confirmed by contact angle measurements and surface chemical analyses using XPS. To accelerate this transition, low-temperature annealing has been widely studied. Heating laser-treated samples in air at moderate temperatures (100-200  ℃) significantly shortens the hydrophilic-to-hydrophobic transition period by facilitating the decomposition and adsorption of airborne hydrocarbons and by reducing the concentration of polar hydroxyl groups on the surface. Another effective and scalable method involves secondary laser treatment. This technique enhances the complexity and dual-scale nature of the surface textures, leading to a more stable Cassie-Baxter state. Furthermore, advanced laser interference strategies, such as direct laser interference patterning (DLIP), can precisely fabricate periodic structures, improving water repellency and surface durability. Hybrid techniques like combining NDLW with ion implantation have demonstrated superior performance. For instance, post-laser carbon ion implantation not only modifies surface energy but also improves mechanical robustness and corrosion resistance, enabling the formation of long-lasting superhydrophobic surfaces suitable for harsh environments. The findings reviewed in this study demonstrate that nanosecond laser-based surface texturing, followed by eco-friendly post-treatments, offers a versatile and sustainable route to engineer functional metallic surfaces without relying on hazardous chemicals. The resulting superhydrophobic surfaces exhibit excellent durability, tunable wettability, and enhanced environmental compatibility. In conclusion, this work outlines the fundamental mechanisms, recent advancements, and technological trends in the field of laser-induced wettability engineering on metallic substrates. It highlights the synergy between laser-generated microstructures and environmentally benign surface modifications, providing a valuable reference for future research and industrial applications aimed at achieving high-performance and sustainable surface functionalities.

The additive manufacturing of 316L stainless steel presents numerous advantages, such as high efficiency, the ability to create complex geometries via freeform fabrication, and superior mechanical and corrosion resistance properties. These characteristics establish a strong foundation for the integrated manufacturing of critical components used in diverse fields, including mining machinery, engineering equipment, hydraulic systems, and other applications that require a seamless blend of structural integrity and functional performance. Despite these benefits, the wear resistance of additively manufactured 316L stainless steel remains a significant challenge that hinders the broad applicability of 316L stainless steel in demanding environments. Ultrasonic severe surface rolling (USSR) is a promising nanocrystallization technology. This innovative technique can generate thick and uniform gradient surface layers while producing exceptionally smooth surfaces on metallic materials, including 316L stainless steel. Importantly, USSR is effective not only on flat surfaces but also on components with complex geometries, showing its potential to significantly enhance the wear resistance of additively manufactured parts. In this study, selective laser melting (SLM) was used to fabricate 316L stainless steel. The SLM was followed by USSR to improve the wear resistance of the 316L stainless steel. A comprehensive microstructural analysis was performed using transmission electron microscopy and electron backscatter diffraction to investigate the microstructural evolution induced by the USSR treatment. The results indicate that the USSR process induced a gradient heterogeneous structure within the surface layer of the SLM-fabricated 316L stainless steel. This gradient heterogeneous structure is characterized by a microstructural transformation from a homogeneous nanograined structure at the surface to a heterogeneous structure with increasing depth. The surface nanograined structure was composed of austenitic grains and a few martensitic grains with an average grain size of 87 nm. In contrast, the SLM-fabricated sample exhibited a heterogeneous structure composed of austenitic grains with a large average grain size of 27 μm. Linear reciprocating sliding tribological tests were conducted using a ball-on-flat plate configuration at room temperature to evaluate wear resistance under both dry friction and emulsion lubrication conditions. The findings reveal a substantial reduction in wear volume under dry friction. The wear volume for the SLM-fabricated sample decreases from 3.58×10^-2 mm³ to 1.90×10^-2 mm³ for the USSR-treated sample, representing a notable reduction of 46.93%. Similarly, under emulsion lubrication, the wear volume decreases from 4.74×10^-4 mm³ to 2.39×10^-4 mm³, representing a reduction of 49.58%. These results unequivocally demonstrate that the USSR method significantly enhances the wear resistance of SLM-fabricated 316L stainless steel. Additionally, microhardness measurements show a marked improvement in hardness, which increases from 237.83 HV to 442.27 HV, representing an impressive enhancement of 86%. Further characterization of the worn surface morphology was conducted using scanning electron microscopy and energy-dispersive X-ray spectroscopy to elucidate the underlying wear mechanisms. The results indicate that the USSR treatment did not fundamentally alter the wear mechanisms of the SLM-fabricated 316L stainless steel. Under dry friction conditions, the worn surface morphology is characterized by high concentrations of elemental oxygen along with visible grooves and pits, suggesting that oxidative wear, abrasive wear, and delamination are the predominant wear mechanisms. In contrast, under emulsion lubrication, the morphology exhibited grooves and pits, indicating that abrasive wear and delamination took precedence in this environment. The observed enhancement in wear resistance is primarily attributable to the increased hardness and deformation resistance resulting from the heterogeneous gradient structure established by the USSR treatment. These findings provide valuable insights and present a novel methodology for enhancing the wear resistance of additively manufactured 316L stainless steel and its associated components, thereby paving the way for its wider adoption in industrial applications. A typical application is the production of durable and highly reliable water-hydraulic components for use in mining machinery.

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.

The development of metal cutting operations for higher speed, precision, and efficiency has led to increasing demands on the performance of cutting tools. Practical experience has shown that improving the overall performance of cutting tools solely through design, manufacturing processes, or material enhancements is difficult and uneconomical. However, modifying the surfaces of cutting tools using surface engineering techniques is an effective means by which to improve the comprehensive performance of cutting tools and machining efficiency. Hence, such methods are receiving increasing attention and acceptance in the manufacturing industry worldwide, and they are being rapidly developed and popularized. Transition metal nitride coatings are widely used in cutting tools, molds, automotive components, and aerospace applications. Compared with pure metal coatings, transition metal nitride coatings exhibit superior mechanical properties, wear resistance, and thermal stability. To improve the service life and milling performance of end mills as well as reveal the mechanisms behind the enhancement of their wear resistance and cutting performance, multi-arc ion plating technology was used to prepare three types of coatings, namely, CrAlN / CrN / Cr, TiAlN / CrN / Cr, and CrAlN / TiAlN / CrN / Cr, on the surfaces of YG6 carbide and three-flute end mills. The preparation techniques, microstructures, performance differences, and mechanisms underlying the improved wear resistance and cutting life of the coatings were investigated. The coating thicknesses of TiAlN, CrAlN, and CrAlN / TiAlN coatings were 2.8, 2.8, and 2.9 µm respectively, as measured by a ball milling tester. The cross-sections of the three coatings were observed using scanning electron microscopy (SEM), which revealed a distinct multilayer structure in the CrAlN / TiAlN coating. Compared with the TiAlN and CrAlN coatings, the CrAlN / TiAlN coating had a lower surface roughness of 19 nm, and the number of large surface particles was reduced. The results of an X-ray diffraction analysis showed that the three coatings had a face-centered cubic structure. The TiAlN coating exhibited a preferential orientation along the (200) plane, whereas the CrAlN and CrAlN / TiAlN coatings displayed a preferential orientation along the (111) plane. The microhardness and adhesion strength of the coatings were measured using a microhardness tester and a scratch tester. The results indicated that the CrAlN / TiAlN multilayer exhibited a hardness of 2 651 HV and an adhesion strength to the substrate of 59.2 N, which are significantly higher than those of TiAlN and CrAlN coatings. The friction and wear behaviors as well as the anti-wear and friction-reducing mechanisms of the three coatings were evaluated using a high-temperature tribometer. The results showed that the CrAlN / TiAlN multilayer coating exhibited superior tribological properties, compared with the TiAlN and CrAlN coatings. At room temperature, the average friction coefficient and wear rate of the CrAlN / TiAlN multilayer coating were 0.603 and 2.92×10^-6 mm³(Nm)^-1, respectively. The primary wear characteristic of the CrAlN / TiAlN coating was adhesive wear. As the temperature increased to 400 °C, the average friction coefficient of the coating decreased to 0.467 while the wear rate slightly increased to 1.31×10^-5 mm³(Nm)^-1. The primary wear mechanisms of the CrAlN / TiAlN coatings were adhesive and abrasive wear. The cutting performance of the uncoated and coated tools with the three coatings was evaluated via the wet milling of 45# steel. The results indicated that the service life of uncoated tools was 32,000 mm³, with a surface roughness of 636 nm for the machined workpiece. In contrast, the service lives of the TiAlN, CrAlN, and CrAlN / TiAlN multilayer-coated tools were extended by 80%, 140%, and 200%, respectively, compared with those of the uncoated tools. The surface roughness of the machined samples decreased to 462, 415, and 402 nm. By observing and analyzing the micromorphology and surface element distribution of the rear cutting face of the tool at different wear stages, it was found that tool tip wear and blunting were the main factors affecting the service life of the milling tool. The tool coating significantly enhances the wear resistance of the tool tip and thereby extends its overall service life.

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.

Marine biofouling, defined as the attachment of marine microorganisms, algae, and barnacles to submerged surfaces, poses a significant threat to ships and marine equipment. Marine biofouling increases fluid resistance, reduces fuel efficiency, exacerbates structural damage, and shortens equipment lifespan. Various antifouling technologies have been developed to address these issues. Despite their effectiveness, traditional organic antifouling coatings, especially those relying on toxic biocides such as tributyltin, have been strictly restricted because of their detrimental impact on the environment. Therefore, the development of efficient, long-lasting, and environment-friendly antifouling technologies is of paramount importance. This study provides a comprehensive review of the development, mechanisms, and recent progress in antifouling technologies. It begins by introducing the formation process and impact of marine biofouling, with a particular focus on traditional organic antifouling coatings. These coatings inhibit biofouling by releasing biocides; however, their application is limited owing to environmental concerns, prompting researchers to seek alternative non-toxic or low-toxicity antifouling approaches. Subsequently, the research status of environment-friendly antifouling technologies, including fouling-release, fouling-resistant, and biomimetic antifouling technologies, is reviewed. Their antifouling mechanisms and characteristics are summarized, and the existing problems associated with each type of antifouling technology are discussed. Fouling-release coatings, which can release fouling organisms by flowing seawater owing to their intrinsically low surface energy characteristics, have been extensively studied. However, the drawbacks of fouling-release coatings, including poor antifouling ability under static conditions, poor mechanical robustness, and low adhesion strength, restrict their widespread use. In terms of fouling-resistant antifouling technologies, biofouling is inhibited by a hydration layer formed at the surface using hydrophilic materials. Although these technologies possess antifouling capabilities, they still face challenges in terms of durability, mechanical strength, and large-scale fabrication. Biomimetic antifouling technologies draw inspiration from the natural antifouling mechanisms of marine organisms, such as sharkskin microstructures, lubricating layers of pitcher plants, and natural antifouling agents. By using micro and nanostructures, liquid lubricating coatings, or natural antifouling components, these technologies can achieve non-toxic antifouling characteristics. These biomimetic antifouling technologies are both biocompatible and sustainable; however, further optimization is required for large-scale production and long-term durability. Additionally, the research status and application prospects of inorganic antifouling technologies with a focus on laser cladding and thermally sprayed antifouling coatings are summarized. Inorganic antifouling coatings fabricated by laser cladding or thermal spraying exhibit significantly superior mechanical robustness and adhesion strength to the substrate compared with organic antifouling coatings, thus being promising. The future development of inorganic antifouling coatings should focus on the fine design and regulation of their microstructures and properties. Based on a comprehensive review of the existing antifouling technologies, this study further dissects the key challenges and future development trends in antifouling research. The future development of antifouling technology should focus on the synergistic use of multiple antifouling techniques to achieve high efficiency, non-toxicity, environmental friendliness, long-term effectiveness, broad-spectrum protection, and the integration of corrosion and antifouling prevention. The development of novel intelligent antifouling technologies, multifunctional biomimetic antifouling methods, long-lasting green antifouling and anticorrosion solutions, and antifouling coatings with self-healing and self-cleaning capabilities is important for meeting diverse antifouling requirements in multiple marine areas and complex operational conditions. This study systematically categorizes antifouling technologies and provides a comprehensive overview of their mechanisms and limitations. It places particular emphasis on the development of environment-friendly and inorganic antifouling technologies, which hold the potential to address the current challenges in the antifouling field. By reviewing the advantages and drawbacks of the various approaches, this study offers valuable insights into the design and implementation of high-performance antifouling technologies. This study provides a solid theoretical foundation for future research.

Glass microlens arrays are widely used in consumer electronics, biosensing, and optical imaging. Glass molding technology is considered a promising manufacturing method for the mass production of glass microlens arrays owing to its efficiency and cost-effectiveness. However, the complex structures of microlens arrays present significant challenges to the molding process, particularly related to non-uniform glass filling and complicated stress distributions, directly affecting the quality of the microlenses formed. This study aimed to optimize the molding process by investigating the glass-filling behavior during microlens array formation through a combination of finite element simulation and experimental study. A finite element model of glass molding was developed to explore the effects of process parameters--such as molding temperature, molding rate, friction coefficient, and lens center spacing--on the filling behavior and stress distribution within microlens arrays. The simulation results revealed that these parameters significantly influenced molding quality, emphasizing the importance of their optimization to achieve uniform microlens arrays. Numerous experiments were conducted to validate the simulation model, demonstrating the consistency between simulated and experimental outcomes, thus confirming the accuracy of the model. Based on these findings, the molding process parameters were optimized, and several conclusions were drawn from the experiments. First, lower molding temperatures decreased glass forming performance. When the molding temperature reached 550 ℃, further increases had minor influence on glass filling performance but reduced internal glass stress. Increasing the molding rate had a minor impact on glass filling capability but tended to increase internal stress. Second, the filling uniformity of microlens arrays was significantly influenced by the friction coefficient at the interface. Reducing the friction factor significantly improved filling uniformity but substantially decreased the filling depth of the microlens arrays. When the friction factor was below 0.1, the internal stress of the glass significantly increased, whereas the stress remained within the range of 25-30 MPa when the friction factor was between 0.1 and 0.3. The distance between the microlens arrays affects the glass filling. An increase in the distance between the microlens arrays results in an increase in the resistance gradient at different lens positions, thereby reducing the uniformity and filling depth of the microstructures while having minimal impact on the internal stress of the glass. Finally, a uniform microlens array was successfully fabricated from a D-ZK2 glass preform using a molding temperature of 550 ℃, molding rate of 0.01 mm / s, and pressing depth of 110 m. The resultant microlens array exhibited a surface roughness (Sa) of 4.2 nm, single lens profile peak-to-valley error of approximately 1.6 μm, and an imaging resolution of 203.2 lp / mm, thus meeting high-performance optical component requirements. This research provides substantial technical support for the mass production of glass microlens arrays and valuable insights into the molding of optical elements with complex structures. As glass molding technology continues to advance and mature, the application of glass microlens arrays is expected to expand across various fields, significantly contributing to the prosperity of the optical industry. This study underscores the significance of process parameter optimization to achieve high-quality molding outcomes. Careful management of molding temperature, rate, and friction is essential for uniform filling and minimal stress concentrations. The validated optimized process can enhance the structural integrity and optical performance of the microlens arrays, critical for the applications of high-resolution imaging and precise light control. In conclusion, combining finite element modeling and experimental validation has proven effective for understanding and optimizing the glass molding process of microlens arrays. These findings contribute to the body of knowledge in precision optics manufacturing and facilitate the development of improved optical components for diverse applications.

As one of the most popular advanced functional ceramics, silicon carbide (SiC) has many excellent characteristics, such as low coefficient of expansion, high thermal conductivity, and radiation resistance. In recent years, brake materials prepared using SiC have been widely used in braking systems such as cars and aircraft. However, owing to its high hardness, SiC is difficult to process using conventional methods. At the same time, the intrinsic hydrophilic characteristics of SiC make its surface prone to fouling and icing. This not only shortens the service life of the material and reduces its utilization efficiency and braking performance but also poses potential safety hazards. These issues limit the broader application of SiC in various fields. Therefore, improving the surface properties of SiC materials through composite processing has become the key to broadening their applications. In this study, a laser-chemical composite processing method was developed to fabricate superhydrophobic SiC surface. First, regular hexagonal and smooth quadrilateral periodic micro-nanostructures were constructed on the surface of SiC materials by nanosecond laser ablation. Subsequently, superhydrophobic surfaces were successfully prepared by further silane-ethanol mixed solution modification and heat treatment. The surface morphology of superhydrophobic SiC materials was characterized by laser confocal microscopy and scanning electron microscopy, and the surface chemical composition was analyzed using energy-dispersive spectrometry and X-ray photoelectron spectroscopy. Furthermore, the influence of the surface structure and surface chemistry on wettability was clarified. Experimental results demonstrated that the surface roughness of the SiC material treated by the composite process increased significantly, forming a regular groove structure. As the laser scanning rate decreased, the depth of the surface grooves gradually increased. This reduction in air retention led to a decrease in the contact area between the water droplets and material surface, thereby affecting the surface wettability. Within a certain range, with the decreases in the laser scanning rate and scanning pitch, the surface wettability was improved, resulting in a composite Wenzel-Cassie state. The maximum contact angle of the material surface was 156.4°, and the minimum rolling angle was 1.3°. The O content on the surface of the untreated SiC material was 2.75%, and the functional groups of C-C and C-Si were the main components. After laser processing, the O content rapidly increased to 28.83%, resulting in a large number of C=O and Si-O-Si functional groups. After laser-chemical composite processing treatment, O accounted for 17.04% of the chemical components on the surface. Simultaneously, a large number of hydrophilic groups, such as C=O and C-O, were decomposed and broken. In addition, the distribution density of Si was notably different. Hydrophilic groups, such as C=O and C-O, were decomposed and fractured, resulting in the formation of a large number of hydrophobic functional groups, such as Si-O-Si. The surface of the superhydrophobic SiC material exhibited several enhanced functional properties. First, its surface could delay icing for over 250 s. Second, its corrosion resistance was significantly improved. Finally, it exhibited excellent self-cleaning performance. Moreover, compared with the smooth quadrilateral structure, the surface roughness of the regular hexagonal micro-nano structure was increased by more than 3 μm. The surface had a more obvious fence structure, and the ability of the grinding wheel to resist cyclic friction was increased by four times. The icing time was delayed by an additional 40 s, and it was completely frozen into ice droplets at 280 s. Therefore, the application requirements of the brake disc were satisfied. As demonstrated by the performance characterization experiments, the surface of the superhydrophobic SiC material exhibited excellent self-cleaning capability, corrosion resistance, icing resistance, and wear resistance. These properties indicate that the laser-chemical composite processing method can be used to prepare superhydrophobic SiC surfaces with stable performance. Ultimately, this process provides a theoretical and practical approach for the preparation of SiC material surfaces with desirable properties, thereby satisfying the application requirements of SiC brake pads. This study utilized fluorine-free chemical reagents, which are known for their low environmental impact and reduced costs. This approach is expected to further establish a foundation for the laser functionalization of SiC materials. It also has the potential to expand the scientific research and engineering applications of SiC materials in various fields.

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.

In recent years, laser cladding for the preparation of high-entropy alloys (HEAs) has attracted widespread attention in aerospace, transportation, and marine applications. FeCoCrNi-series high-entropy alloys are among the most widely studied transition-metal HEAs. Due to their unique properties (i.e., high-entropy effect, lattice distortion effect, slow diffusion effect, and cocktail effect), FeCoCrNi-series entropy alloys can achieve synergistic improvement in strength and toughness. Many studies have confirmed that laser-cladding FeCoCrNiAlTi HEA coatings offer excellent mechanical properties, including high strength, toughness, corrosion resistance, and oxidation resistance at high-temperatures. However, there are currently few studies on the friction and wear mechanism of FeCoCrNiAlTi HEA coatings under corrosion-friction coupling, and the interaction between alloy elements, microstructure, wear, and corrosion resistance remains unclear. In this study, a FeCoCrNiAl_0.5Ti_0.5 HEA coating was prepared on an AISI 1045 steel substrate using laser-cladding technology. Dry and wet friction tests were performed on the coating and substrate immersed in the solution for different durations. The dry and wet friction was tested using a ball-on-disc wear test. After grinding and polishing, the microstructure of the sample surface was characterized, followed by corrosion in an aqua regia solution (75 mL HCl and 25 mL HNO₃ per 100 mL solution) for 30 s. The hardness pits of the sample and the transition from the coating to the substrate were observed via optical microscopy (OM). After the wear test, the depths and widths of the wear scars were measured using a three-dimensional profilometer. The microstructures and wear scar characteristics of the samples were characterized using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscope (EDS) and an electron backscatter diffraction (EBSD) detector. The phase compositions of the powder and sample were characterized using X-ray diffraction (XRD). The dry and wet friction behaviors of the coating related to atmospheric and corrosive environments were investigated in combination with the friction and wear test results. The results indicated that the microstructure of the laser-cladded FeCoNiCrAl_0.5Ti_0.5 HEA coating mainly consisted of a dendrite region (DR) with a body-centered cubic (BCC) phase and an interdendritic region (IR) with a face-centered cubic (FCC) phase. In addition, under spinodal decomposition, a portion of the BCC phase in the lamellar eutectic structure of the coating transformed into the L2₁ phase. The laser-clad FeCoNiCrAl_0.5Ti_0.5 HEA coating demonstrated excellent wear resistance. The friction factor of HEA coating and the dry friction factor of AISI steel substrate were 0.69 and 0.75, respectively, with wear rates of 5.04×10^-5 mm³ / (N·m) and 1.41×10^-4 mm³ / (N·m), respectively. The immersion time in a 3.5wt.% NaCl solution significantly influenced the wet friction and wear properties of the laser-cladded FeCoNiCrAl_0.5Ti_0.5 HEA coating. The wet friction wear rate of the coating increased with the immersion time. The wet friction wear rate of the unimmersed coating was 1.11×10^-5 mm³ / (N·m), while that of the coating immersed for 15 days increased by 1.77 times, reaching 3.08×10^-5 mm³ / (N·m). The main forms of dry friction and wear of the laser-clad FeCoNiCrAl_0.5Ti_0.5 HEA coating were three-body wear and abrasive wear, whereas the wet friction wear process was affected by corrosion, oxidation wear, and three-body wear. The wet friction wear process is lubricated by water and oxide films between the friction pairs; therefore, the wear rate is significantly lower than that in dry friction. However, under wet friction conditions, the oxide film was easily corroded, leading to the formation of microcracks and film delamination, ultimately resulting in three-body wear.

In the context of the national strategy for “Maritime power” and the construction of the “Belt and Road”, marine engineering infrastructure construction of China has accelerated. The on-site use of raw materials such as coral and seawater to prepare marine concrete (MC) significantly reduces project costs, ensures the construction period, and reduces carbon emissions due to transportation. However, complex and harsh marine environments have a strong corrosive and destructive effect on structures, seriously affecting the use and safety of marine engineering structures. Therefore, it is of great significance to apply additional anticorrosion measures to MC structures and conduct research on service life prediction and durability design. In marine environments, the corrosion of steel bars inside concrete structures caused by chloride ions in seawater is a main reason for the deterioration in the durability of these structures. In this study, to effectively improve the durability of concrete structures in marine engineering, it was treated with two anti-corrosion measures: internal addition of composite active mineral admixtures (MA) and external application of high-permeability epoxy protective materials (SP). By investigating the diffusion law of Cl^- in concrete, the effects of thicknesses of concrete protective layers, concrete types, strength grades, exposed areas, and additional anti-corrosion measures on the service life of coral aggregate concrete (CAC) and ordinary aggregate concrete (OAC) structures were studied. Design suggestions for improving the service life of MC structures were proposed based on the ChaDuraLife life prediction method, which combines the characteristics of the exposed environment of concrete structures in marine engineering. Theoretical and data support are provided for the application of MC in practical engineering. The results showed that under the same marine exposure zone, with an increase in the concrete strength grade and protective layer thickness, the service life of the CAC and OAC structures gradually increased. The service life of the OAC structures exhibited the trend of underwater zone > atmospheric zone > tidal zone in different ocean exposure areas. When the concrete strength grade, protective layer thickness, and exposure zone were the same, the service life of CAC structures was shorter than that of OAC and followed the pattern of atmospheric zone > underwater zone > tidal zone. The use of internally mixed composite mineral admixture MA, externally coated high-permeability epoxy protective material SP, and “internally mixed + externally coated” anti-corrosion measures increased the service life of OAC structures by 1.8/1.7, 2.4/2.4, and 3.4/3.2 times, respectively, compared with no measures. In underwater zone of the ocean, for CAC/OAC structures with a conventional protective layer thickness of 6 cm, even if the concrete strength grade reached C50, the service life remained relatively low. Additional anticorrosion measures, such as internal mixing and external coating, were required to improve the durability of the structure. Considering factors such as engineering costs and structural durability, the adoption of OAC structures for nearshore engineering is recommended. When the concrete strength grade is C50 or higher, the protective layer thickness is greater than 14 cm, and when the high-permeability epoxy protective material SP is applied externally, the service life of the underwater structure can reach up to 100 years. It is recommended that CAC structures be used in offshore engineering applications. When the concrete strength is greater than C65 and the thickness of the protective layer is 10 cm, the combined anti-corrosion measure of mixing MA and coating SP can significantly improve the service life of the engineering structure.

High-speed dry cutting technology is widely used in the manufacturing industry because of its high machining accuracy, good surface quality of machined workpieces, and environmental friendliness. However, the tools used for high-speed dry cutting suffer from severe thermal and mechanical effects. To improve the cutting performance of coated tools for the high-speed dry machining of titanium alloys, AlCrBN / AlTiN multilayer coatings with different numbers of bilayers were synthesized on cemented carbide cutters using an arc ion plating technique. The microstructures and mechanical properties of the multilayer coatings were characterized by SEM, XRD, Knoop micro-hardness test, and Rockwell indentation test. The thermal stability, tribological, and wear behaviors were investigated via vacuum annealing and ball-on-disk tribological tests. A CNC turning lathe was adopted to assess the high-speed dry turning performance of the multilayer coated cutters, and the wear behaviors of the coated cutters during the machining of a Ti alloy were studied in detail. The thicknesses of AlTiN, AlCrBN-5 (bilayer number of 5), and AlCrBN-10 (bilayer number of 10) coatings were of the order of ~3.0 μm. All coatings adhered well to the substrate. The AlCrBN / AlTiN coatings could be divided into three parts: the bottom layer was a Cr+CrN adhesion layer, the middle layer was an AlTiN transition layer, and the top layer was an AlCrBN / AlTiN working layer. The results revealed that all AlCrBN / AlTiN multilayer coatings were composed of fcc-(Cr, Al)N and fcc-(Ti, Al)N solid solution phases, and the AlCrBN-10 coating exhibited the highest hardness of 4470.1±144.2 HK_0.05 and a high adhesion level of HF1. A high-temperature annealing experiment showed that the microhardness of the coatings increased slightly after annealing at 800 ℃. A further increase in the annealing temperature to 1000℃ resulted in phase decomposition and a sharp decrease in microhardness. The AlCrBN / AlTiN multilayer coating exhibited the highest temperature stability. The AlCrBN / AlTiN multilayer coating maintained a microhardness up to approximately 2790 HK_0.05 after annealing at 1000 ℃. The lowest coefficient of friction (0.56) and wear rate (0.21×10^-15 m³·N^-1·m^-1) were achieved for the AlCrBN-10 coating under abrasive and oxidation wear during ball-on-disc tribological experiments. High-speed dry cutting tests revealed that the lifetimes of the AlCrBN-5 and AlCrBN-10 coated cutters were 15 and 14 min at a cutting speed of 100 m / min, increasing by 25% and 17%, respectively, compared to the AlTiN coated cutter. When the cutting speed was further increased to 150 m / min, the AlCrBN-10 coated cutter (280 s) exhibited a greater improvement of 250 % in lifetime compared with the AlTiN coated cutter (80 s). The AlTiN coating showed limited improvements in hardness, adhesive strength, and high-temperature performance, resulting in rapid failure under more severe cutting conditions. The AlCrBN-10 coating had the highest hardness, thermal stability, and adhesive strength and can effectively resist coating peeling and thermal shock under high cutting speed parameters, greatly improving the cutting life of the coated cutters. Various cutting stages, including initial, middle, and failure stages, were observed using scanning electron microscopy and energy dispersive spectroscopy to investigate the wear mechanism evolution during high-speed dry turning. The wear mechanisms of all as-studied coatings were adhesion and oxidation on both the rake and flank faces regardless of cutting speed, whereas the AlCrBN / AlTiN multilayer coated cutters showed significantly enhanced resistance to adhesion and oxidation, which could account for their improved cutting performance during high-speed dry machining against Ti-6Al-4V alloy. The AlCrBN / AlTiN multilayer coating can effectively improve the high-temperature and cutting wear properties of the tool surface and has potential applications in high-speed dry cutting.

Ti(C, N)-based cermets are important materials for cutting tools because of their excellent hardness, wear resistance, and high-temperature deformation resistance. However, the metal binder phase in Ti(C, N) cermets easily induces adhesive wear, elemental diffusion, and softening at high temperatures during high-speed machining. These problems can deteriorate the tool performance, thus limiting the further promotion and industrial application of Ti(C, N)-based cermet cutting tools. Physical vapor deposition (PVD) is an effective method for enhancing the properties of Ti(C, N)-based cermets. In this study, AlTiN and AlTiN / AlCrN coatings are deposited on Ti(C, N)-based cermet tools via cathodic arc evaporation. The effects of the surface coatings on the mechanical, friction, oxidation, and cutting properties of Ti(C, N)-based cermets are systematically investigated using X-ray diffraction, scanning electron microscopy, Rockwell hardness tests, nanoindentation tests, wear tests, oxidation experiments, and turning tests. Experimental results show that both the AlTiN and AlTiN / AlCrN coatings exhibit a single-phase face-centered cubic structure, with hardness values of 33.9±0.8 and 36.1±1.6 GPa, respectively, which are significantly higher than that (27.4±1.7 GPa) of uncoated Ti(C, N)-based cermets. Additionally, the surface coatings improve the fracture toughness of Ti(C, N)-based cermets, as shown by an increase from 9.8 ± 0.18 MPa∙m^1/2 for the uncoated cermet to 10.5 ± 0.08 and 10.8 ± 0.05 MPa∙m^1/2 for the AlTiN- and AlTiN / AlCrN-coated cermets, respectively. The surface coatings with higher hardness and H³ / E² ratios significantly improve the wear resistance of the Ti(C, N)-based cermets, among which the lowest wear rate of 2.8 × 10^-6 mm³ / (N∙m) is achieved by the AlTiN / AlCrN-coated Ti(C, N)-based cermets. Furthermore, the Ti(C, N)-based cermets coated with AlTiN and AlTiN / AlCrN demonstrate excellent oxidation resistance, and their oxide-layer thickness reduces to ~185 and ~65 nm after oxidation at 800 C for 5 h, respectively. Owing to their combination of higher hardness, lower friction coefficient, and excellent oxidation resistance, the Ti(C, N)-based cermet tools coated with AlTiN / AlCrN exhibit a cutting life that is ~75% higher than that of the uncoated tools. This study reveals the effect of surface coatings deposited via PVD on the wear resistance, high-temperature oxidation resistance, and cutting life of Ti(C,N)-based cermets, which can be applied to improve the comprehensive performance of Ti(C,N)-based cermets. These findings provide a theoretical basis and technical support for the development and design of high-performance Ti(C, N)-based cermet tools and further promote their large-scale application in high-speed machining.

Fe-based amorphous alloys have attracted the attention of researchers due to their excellent mechanical and soft magnetic properties, wear resistance, and corrosion resistance. The short-range order and long-range disorder characteristics of the amorphous structure play important roles. However, the room-temperature brittleness and size limitations of Fe-based amorphous alloys seriously limit their practical applications in surface protection. By overcoming the room-temperature brittleness and size limitations of amorphous alloys, Fe-based amorphous coatings can be prepared using coating technologies such as thermal spraying and laser cladding. These coatings retain high hardness, wear resistance, and corrosion resistance, enabling their application in surface protection of parts. Therefore, this study systematically summarizes the current research status of Fe-based amorphous coatings. In this paper, the recent research progress on Fe-based amorphous coatings is discussed from four aspects: coating materials, coating preparation technologies, wear and corrosion resistance, and practical applications. The results showed that among Fe-based amorphous coating materials, the "Fe-ETM-LTM-M" type Fe-based amorphous alloy powder has the highest glass-forming ability. The Fe-based amorphous alloy powder prepared by the atomization method has a smooth surface and a moderate particle size range, making it most suitable for the preparation of Fe-based amorphous coatings. The coating prepared by thermal spraying exhibited a uniform composition and dense structure. Coatings prepared using laser cladding technology can form metallurgical bonds with the substrate, resulting in high bonding strength. In addition, coating preparation techniques such as detonation spraying, cold spraying, and magnetron sputtering have also been used to produce Fe-based amorphous coatings. Therefore, thermal spraying and laser cladding have become the two most commonly used technologies for preparing Fe-based amorphous coatings, and the performance of these coatings can be improved through appropriate technical adjustments or the addition of auxiliary fields. Technical adjustments can be achieved by modifying the structure of the spraying device to obtain a higher heat source temperature or increase the particle flight speed. The addition of an auxiliary field—such as coupling an ultrasonic vibration field or an electromagnetic field outside the coating preparation device—can reduce the number of cracks in the prepared Fe-based amorphous coating. During the coating preparation process, factors such as element composition, the addition of reinforcing phases, and pre / post-treatment procedures contribute to improving the wear and corrosion resistance of Fe-based amorphous coatings. For example, low-temperature cyclic treatment can induce structural relaxation in the coating without causing recrystallization, while the regulation of elemental composition can enhance the stability of the passivation film formed on the coating surface. Moreover, the addition of hard phases—such as WC—effectively blocks the propagation of shear bands and enhances the wear resistance of Fe-based amorphous coatings. Pores not only serve as primary channels for corrosive substances to penetrate the coating but also act as the initial sites of surface damage under friction and wear. Sealing treatments can effectively reduce the number of pores in Fe-based amorphous coatings, thereby expanding their application prospects under complex working conditions. Fe-based amorphous coatings have played a key role in the military and nuclear industries, power equipment protection, and other fields, thanks to performance enhancements developed by scientific and technical personnel. These four aspects illustrate the performance improvements and current practical applications of Fe-based amorphous coatings from different perspectives, providing a valuable reference for researchers and engineers involved in their development.

Laser-directed energy deposition (LDED) is a prominent technology in laser additive manufacturing and is known for its ability to enable the fabrication of complex, high-performance components layer by layer. The high-energy laser beam melts the substrate material, and the powder feeder simultaneously conveys the metal powder into the melt pool to deposit and solidify materials in a controlled manner into the required components The melt-pool temperature is crucial in determining the quality of the final component because it affects the microstructure, mechanical properties, and overall morphology of the deposition. During LDED, the temperature of the melt pool fluctuates owing to several variables, including changes in heat dissipation from the component, external environmental conditions, and equipment variations. These temperature fluctuations can result in defects such as unsatisfactory bonding, distorted geometry, or inconsistent material properties in the final component. Therefore, precise and real-time monitoring of the melt-pool temperature is essential to ensure that the deposition process remains within the optimal operating conditions, thus guaranteeing high-quality component production. The core challenge with LDED is the precise measurement and control of the melt-pool temperature. Measuring temperature directly is challenging owing to the dynamic and high-temperature nature of the melt pool, and conventional temperature-measurement methods may not be applicable or sufficiently precise in such environments. Hence, a color charge-coupled device coaxial temperature-measurement system is developed. This system allows real-time detection of the temperature distribution in the melt pool and provides important data for regulating the process parameters and maintaining the desired temperature profile during deposition. Several factors can affect the melt-pool temperature during LDED, including the powder feed rate, scanning speed, and laser power. A high laser power results in more melting and increases the melt-pool temperature, whereas lower power levels can lower the temperature and result in incomplete melting. Similarly, fluctuations in the powder feed rate and scanning speed can further affect the thermal conditions of the melt pool, thus resulting in temperature changes that may require real-time adjustments. To manage these temperature fluctuations and maintain a consistent process control, a closed-loop control system is required. In this study, an incremental fuzzy proportional-integral-derivative (PID) control algorithm is proposed to effectively control the melt-pool temperature. Fuzzy logic integrated into the PID control algorithm can address the nonlinear and uncertain aspects of LDED. It allows the control system to adapt to fluctuations and disturbances more effectively than conventional PID control methods. Simulink is used to develop a melt-pool temperature control simulation system that provides a theoretical framework to support the control-system design. The simulation allows various process parameters to be tested and the response of the control system to be evaluated under different operating conditions. The effectiveness of the control algorithm is verified through practical experiments, in which the laser power and powder feed rate are adjusted to simulate potential challenges in actual production scenarios. The results show that the fuzzy incremental PID algorithm performs better than the standard incremental PID algorithm, reduces the overshoot and steady-state errors, and improves the overall response time in a dynamic environment. This study contributes to the advancement of LDED technology by providing a novel approach for controlling the melt-pool temperature. By incorporating fuzzy logic into the PID algorithm, the system can manage the complex and nonlinear nature of LDED more accurately, thus ensuring consistent component quality and reducing the risk of defects. The closed-loop control system developed in this study has significant potential for real-world applications, as well as provides a robust solution for addressing temperature fluctuations and improving the reliability of laser additive-manufacturing processes.