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.

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.

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 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.

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.

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

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

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

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

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

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

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

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

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

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.

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

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

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

The spent fuel pool is a square structure that requires different welding positions to repair crack defects in stainless steel cladding. However, domestic research on the repair of defects in the wall position of the spent fuel pool is limited. Vertical welding is commonly used for large, heavy structural parts, but because of its welding position, it is prone to issues such as unstable transitions of the molten droplet and downward flow of the molten pool, resulting in weld porosity, lack of fusion, and other defects. By contrast, laser welding features low heat input and rapid cooling, which effectively mitigates the downward flow of the molten pool and reduces the impact of the vertical position of the weld caused by the weld. Local dry underwater welding technology combines the advantages of high weld quality of dry underwater welding and the simplicity of wet welding, which is the current preferred method for the underwater repair of nuclear power plants. Therefore, this study examined crack defects on the wall surface of a spent fuel pool by combining local dry underwater welding technology with laser vertical welding. S32101 duplex stainless steel was used as the base material, and bevel filler tests were conducted on a 4-mm U-shape bevel in both air and underwater environments. The organization and properties of the vertical weld in the two environments were analyzed comparatively. The results showed that compared with the air environment, the heat-affected zone of the weld in the underwater environment was smaller, with less austenite precipitation and insufficient growth in the cladding zone. The ferrite content in both the air and underwater environments was ranked as follows: HAZ > covered weld channel > undercut weld channel > filler weld channel. The overall ferrite content in the cladding zone was higher in the underwater environment as compared with that in the air environment. This difference was due to the greater degree of supercooling and faster cooling rate underwater, which prevented sufficient precipitation of austenite, resulting in a lower overall austenite content. XRD test results indicated that the cladding layer in both environments contained of both ferrite and austenite phases. The hardness distribution of the welds in both environments was consistent, following the order of melt-covered zone > heat-affected zone > parent material. The hardness of each area in the melt-coated layer was slightly higher than that of the filler channel, whereas the filler channel was slightly higher than the bottoming channel. Overall, the hardness of the welds in the underwater environment was higher than that of air-environment welds. Compared with the air environment weld, the tensile strength and impact work of the underwater environment weld decreased but still exhibited good mechanical properties. The impedance spectra and polarization curves from electrochemical corrosion experiments demonstrated that the corrosion resistance of underwater environment welds is lower than that of air-environment welds but still better than that of the base material. In summary, the underwater environment affects the organizational composition, mechanical properties, and corrosion resistance of the weld to varying degrees. However, its overall performance still surpasses that of the base material. This indicates that local dry underwater laser welding technology is highly feasible for the repair of spent fuel pool cladding walls in nuclear power plants, and the research results can provide theoretical and experimental foundations for in-service repair of the spent fuel pool walls.

Icing is a major problem faced by aircraft flying at high altitudes in cold and humid conditions and poses a tremendous threat to the flight safety of aircraft. Research and development of new deicing technology is thus of great importance. Electrothermal deicing is a new type of deicing technology that uses electric heating elements to heat a composite substrate, effectively solving the problem of high energy consumption of current hot-air deicing technology used in aircrafts. In addition, in combination with a fiber metal laminate (FML), which has the characteristics of easy preparation and excellent mechanical properties, a new type of laminated material that utilizes high-resistance stainless steel foil tape and a carbon fiber prepreg composite is proposed. The surface-pretreated FeCrAl is sequentially laminated with glass fiber (GF) and a carbon fiber epoxy resin prepreg (CFRP) and then cured by hot pressing in a vacuum environment. The interfacial bonding condition of the FML is characterized by scanning electron microscopy observation of the cross-sectional morphology of the laminates and by tensile shear tests on the prepared single-layer tensile shear specimens. The metal-fiber interface is well bonded in the FML cross-section at a magnification of ×2000 without delamination. Fewer holes and cracks are present in the resin matrix, and the tensile shear strength of the single-lap tensile shear specimen can reach 7.1 MPa. Results show that the pretreatment of the metal surface can effectively improve the interfacial bonding strength of the FML. Different electrodes and loading methods produce different contact resistances at the current input, and the magnitude of the contact resistance affects the local temperature of the load. Therefore, the effects of three electrode loading methods, namely, double-sided conductive copper foil tape, a copper foil strip, and conductive silver paste combined with a copper foil strip, on the contact resistance are investigated separately. The output voltages of the pulsed power supply fed with a constant 10 A DC current feedback under each of the three methods show that the poor conductivity of the epoxy resin in the conductive silver paste and copper foil tape result in a higher contact resistance of the system than that of the direct contact when using only the copper foil strip. Therefore, using a direct-contact copper foil strip as the electrode loading method in electrothermal testing is appropriate. The electrical and thermal performances of the FML are tested at different power densities. The temperature change curve of the FML is recorded using thermocouples, and the temperature distribution after stabilization is observed using a thermal imager. The tests show that the FML can increase from room temperature to 65 ℃ in 10 min at a power density input of 0.164 W / cm² at a uniform temperature distribution. The static electrothermal process of the FML is simulated using ABAQUS, and the simulation results are in close agreement with the experimental data. The deicing performance of the FML is tested in a low-temperature environment by applying heat to the plate via a 20 A constant DC to the accumulated ice, and the FML can completely melt the accumulated ice within 260 s. The fatigue performance of the FML is tested by repeated electrified heating followed by cooling. After 30 cycles of electrified heating, the electric heating performance of the FML does not change, and the test shows that the excellent fatigue performance of the FML can solve the problem of performance degradation of deicing coatings under repeated use. The research thus shows that FMLs have excellent electric heating, fatigue, and deicing performance and offer the advantages of easy preparation, high specific strength, and high specific stiffness. FMLs can therefore be used as deicing materials for aircraft wing skins.

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

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

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

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

Blending hydrogen with natural gas is an effective method for improving the energy content per unit volume of natural gas and reducing greenhouse gas emissions, as hydrogen serves as a green and clean energy carrier. However, the presence of hydrogen poses a significant challenge for pipelines: hydrogen embrittlement (HE). Hydrogen can permeate into the metal, deteriorating its mechanical properties, particularly in welded joints, which are particularly vulnerable to HE due to factors such as inhomogeneous microstructures and oxide inclusions. To date, however, the relationship between the microstructure of each subzone of a welded joint and its intrinsic susceptibility to hydrogen embrittlement has not been thoroughly investigated. In this study, electrochemical hydrogen charging was employed to investigate the hydrogen damage behavior of high-strength X100 pipeline steel weldments in the absence of external stress. Combining microstructural characterization techniques—such as optical microscopy, laser scanning confocal microscopy, electron backscattering diffraction (EBSD), and quantitative analyses of hydrogen damage levels at each subzone of the welded joint allowed for a detailed exploration of the intrinsic susceptibility of each subzone's microstructure to HE. The results showed that, after identical hydrogen charging, the hydrogen escape velocity varied among different subzones, decreasing in the following order: base metal, heat-affected zone, and weld metal. According to the surface hydrogen damage modes observed, hydrogen blisters were identified as the primary damage mode for the base metal, exhibiting a height of several micrometers and a diameter of several millimeters. In contrast, hydrogen-induced cracking occurred in the weld metal and heat-affected zone on the sample surface, rather than hydrogen blister damage. With increasing current density, both the size and number of hydrogen blisters notably increased, accompanied by severe hydrogen-induced cracking in the cross-section. Quantitative analyses revealed that the weld metal exhibited excellent resistance to hydrogen damage, whereas the base metal was the most susceptible to hydrogen damage when the current density was insufficiently high. However, when a high current density (e.g., 80 mA / cm²) was applied, multiple hydrogen cracks appeared in the coarse-grained heat-affected zone, making it the most susceptible subzone to hydrogen embrittlement. The high resistance of the weld metal to HE is primarily attributed to the presence of acicular ferrite, which possesses a complex and effective grain structure with an extremely low volume fraction of random boundaries. This configuration allows for a more uniform distribution of diffusible hydrogen atoms in the weld metal, resulting in a hydrogen diffusion coefficient that is generally lower than that in the base metal. In contrast, the hydrogen-induced cracks in the base metal consistently nucleate at the pancaked prior austenite grain boundaries, indicating that these boundaries are preferred sites for crack nucleation due to the abundance of inherited deformation dislocations. Moreover, the parallel bainitic block boundaries create rapid diffusion paths for atomic hydrogen across the pancaked prior austenite grains, facilitating the propagation of hydrogen-induced cracks along the rolling direction. Consequently, closer attention should be given to the base metal under relatively low hydrogen fugacity conditions. When hydrogen fugacity is sufficiently high, the heat-affected zone (HAZ) becomes the most susceptible subzone to HE, particularly in the coarse-grained HAZ. This study provides crucial insights into the weakest links within welded joints and offers predictive tools for assessing structural integrity under varying hydrogen fugacity conditions.

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

Bearings, as the core components of mechanical equipment, reduce friction and ensure rotational accuracy. Bearing steels, which are critical materials for the realization of advanced bearings, must have a long service life and high reliability. With the rapid development of the aerospace and military fields, the local temperature of bearings in aircraft engines, high-speed-train bogies, and rapid-fire weapon systems can reach 350 ℃ or higher. This exceeds the upper temperature limit of conventional bearing steels such as GCr15 and M50NiL. Thus, third-generation bearing steel, exemplified by CSS-42L high-alloy steel, which exhibits excellent corrosion resistance and fracture toughness, has been developed in recent years. It is known that friction and wear damage on the surface of bearing steel under rolling contact are the main factors causing failure of bearing components at elevated temperatures.Researchers found that gradient nanograined (GNG) materials can effectively reduce friction and wear damage by preventing surface roughening and the formation of brittle tribo-layers. However, there is limited research on the tribological behavior of GNG CSS-42L bearing steel at elevated temperatures. In this study, GNG CSS-42L bearing steel was fabricated using surface mechanical rolling treatment. The effect of the gradient nanostructure on the tribological properties of CSS-42L bearing steel was investigated. By also analyzing wear morphology and subsurface microstructure evolution, the corresponding friction and wear mechanisms were clarified. The average grain size of the topmost layer of the GNG CSS-42L bearing steel was 25 nm, which gradually increased with the depth from the surface. The grain size at a depth of 100 μm reached 500 nm or more. Notably, the entire GNG layer exhibited a martensitic structure. High-temperature friction tests within the temperature range of 25-500 ℃ were conducted on the coarse-grained (CG) and GNG CSS-42L bearing steels. The factor of friction of CG CSS-42L decreased from 0.64 to 0.43 as the temperature increased to 500 ℃, and the wear rate initially increased to 3.5×10^?5 mm³ / (N·m) at 350 ℃ and then decreased to 6×10^?6 mm³ / (N·m) at 500 ℃. Compared to CG bearing steel, the factor of friction of GNG CSS-42L bearing steel was lower than 0.2 at 25 and 200 ℃, then increased to 0.45 at 500 ℃. The wear rates of GNG CSS-42L at 25 and 200 ℃ were 3.8×10^?6 and 3.66×10^?5 mm³ / (N·m), respectively, much lower than those of CG CSS-42L bearing steel. As the temperature increased to 500 ℃, the wear rates of both CG CSS-42L and GNG CSS-42L bearing steels tended to be comparable. The surface morphology of wear scars showed that the proportion of the oxidation layer in the wear scars increased with the wear temperature. This indicates a transition in the wear mechanism of the GNG CSS-42L bearing steel from abrasive wear to oxidation wear as the temperature increased from 25 to 500 ℃. Subsurface microstructure evolution results demonstrated that the original surface gradient structure remained stable within the range of 25-350 ℃. It is believed that the excellent synergy of strength and ductility, along with the strain accommodation in the GNG layer, suppresses surface roughening and the formation of wear debris, leading to enhanced wear resistance. At 500 ℃, the original gradient structure was fully replaced by a nanograined oxidation layer with a thickness of 3 μm during the wear process. Under friction pair contact, microcracks nucleated and propagated in the oxidation layer, causing the spalling of oxidation debris and increased surface roughness. Thus, the factor of friction and wear rate sharply increased at 500 ℃. These results provide an experimental basis and theoretical foundation for prolonging the service life of bearing components at elevated temperatures.

With the dramatic increase in the demand for medical implant materials, the TC4 titanium alloy can be used as a replacement material for bone tissue owing to its excellent biocompatibility and corrosion resistance. However, the TC4 titanium alloy has poor antibacterial properties, and there may be a higher risk of bacterial infection after implantation in the human body. Coatings prepared by micro-arc oxidation technology have excellent binding strength and can reduce the risk of bacterial infection of titanium alloys by doping with antimicrobial elements. To improve the protective properties of the TC4 titanium alloy in simulated body fluids (SBF), a constant-voltage mode was adopted, with a voltage of 450 V, frequency of 800 Hz, duty cycle of 6%, and time of 10 min. An Sn-doped micro-arc oxide coating was prepared on a titanium alloy by varying the concentration of Na₂SnO₃ in the electrolyte. The microscopic morphology and elemental content distribution of the micro-arc oxide coating were studied using a scanning electron microscope with an attached energy dispersive spectrometer, and the phase compositions and compositions of the micro-arc oxide coatings were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The wear resistance, corrosion resistance, and antibacterial properties of the micro-arc oxide coating in SBF were studied using friction and wear, electrochemical, and antibacterial tests. The results show that the number of pores on the micro-arc oxide coating surface increases after the addition of Na₂SnO₃. With an increase in the Na₂SnO₃ concentration, the number of micropores on the surface of the micro-arc oxide coating decreases until they disappear, small particles appear, and the film becomes increasingly dense and uniform. The main components of the micro-arc oxide coatings are TiO₂, SiO₂, and SnO₂. The friction factor of the micro-arc oxide coating without Na₂SnO₃ is lower than that of TC4. The friction factor of the Sn-doped micro-arc oxide coating in SBF decreases with an increase in the Na₂SnO₃ concentration, and the width of the wear mark is narrowed. When the concentration of Na₂SnO₃ is 10 g / L, the Sn-doped micro-arc oxide coating has the smallest friction factor and the narrowest wear mark width of 198.85 μm, which exhibits the best wear resistance, which may be due to the enrichment of small particles and the lubricating effect. However, the micro-arc oxide coating does not improve the corrosion resistance of the TC4 titanium alloy, which may be caused by the presence of micropores and other defects on the surface of the coating and the lower corrosion resistance of SnO₂ than that of TiO₂. The antibacterial properties of the micro-arc oxide coating improve after the addition of Na₂SnO₃; the Sn-doped micro-arc oxide coating prepared at a concentration of Na₂SnO₃ of 10 g / L and the antibacterial properties of the Sn-doped micro-arc oxide coating are the best in SBF. The optical density value decreases from 0.289 to 0.136 in the Staphylococcus aureus solution and from 0.331 to 0.171 in the Escherichia coli solution, because SnO₂ could inhibit the growth of bacteria. These results provide experimental support for the application of titanium alloys in the field of biomedicine.

Crystallizers are the core components of continuous casting equipment, and their quality directly impacts billet quality and production efficiency. With the advancement of high-drawing-speed continuous casting technology, higher performance requirements for crystallizers have been proposed, particularly concerning wear, a major cause of crystallizer copper plate failure. Currently, electroplated crystallizer coatings hold approximately 80% of the market share. However, the long deposition cycle, low hardness, tendency for coating peeling, and environmental pollution caused by electroplating technology make it inevitable for this technology to be phased out. Supersonic flame spraying (HVOF) is one of the most widely used thermal spraying technologies, capable of producing highly dense and uniform coatings due to its fast flame flow rate, high powder kinetic energy, and low oxidation levels. In addition, the HVOF technology offers a wide range of material options and can be functionally designed to accommodate different sizes and parts of the crystallizer, meeting continuous casting requirements. A NiCrCoBSi multiple principal element alloy coating has been applied to the surface of crystallizer copper plates using HVOF technology to improve their high-temperature wear performance of copper plates. The microstructure of the NiCrCoBSi coating was studied using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The wear resistance of the coatings was evaluated using frictional wear equipment and compared with that of the commonly marketed electroplated NiCo coating. Additionally, the wear mechanisms of the coatings were analyzed. The results showed that the NiCo coating had a single-phase face-centered cubic solid solution structure, whereas the NiCrCoBSi coating exhibited an FCC solid solution, with CrB and M₂₃C₆ as the main phases. Both coatings had high densities with no observed cracks. A clear delamination was found between the NiCo coating and the copper alloy substrate, with no transition zone, indicating a mechanical bond. In contrast, a diffusion layer between the NiCrCoBSi coating and the copper alloy substrate due to diffusion heat treatment after spraying, resulting in the formation of a metallurgical bond. Compared to NiCo coating, NiCrCoBSi coating exhibited a 95% increase in hardness, whereas the fracture toughness decreased by only 5.4%. The friction factor of the NiCo coating fluctuated significantly, ranging from 0.4 to 1.0, and eventually stabilizing around 0.6. Compared with the NiCo coating (0.67), the friction factor of NiCrCoBSi coating is lower (0.51), with the curve showing good stability, ranging from 0.4 to 0.6, and ultimately stabilizing at around 0.52. After wear, the surface of the NiCo coating exhibited large flakes accompanied by dark gray adhesive marks, cracks, and debris. The worn surface of the NiCrCoBSi coating showed signs of debris, peeling, furrowing, and adhesive wear, with many small peeling pits. The wear mechanisms of both coatings were adhesive and fatigue wear, accompanied by a small amount of abrasive wear. The wear rate of NiCrCoBSi coating was 1.53×10^?5 mm·N^?1 ·m^?1 , which is about five times higher than that of NiCo coating (7.91×10^?5 mm·N^?1 ·m^?1 ). The main reasons for the higher wear resistance of the NiCrCoBSi coating are the better hardness, various wear-resistant phases, and the work hardening of the wear surface layer. This hardening occurs due to the plastic deformation of the coating under cyclic loading, during which the hard phases of the coating were cut and rotated. The carbides and borides are refined and spheroidized, enhancing the hardness of the wear surface layer. This research paves the way for developing coatings with excellent wear resistance for copper and their alloys.

The high-speed rub between the rotating and stationary parts of compressors plays a crucial role in the safe operation of aero engines. Extensive research has been reported on high-speed friction issues concerning compressor rotors and stators. Nevertheless, systematic reviews of relevant research progress have been lacking. This issue must be examined from the perspective of high-speed friction wear and energy-dissipation mechanisms so as to ensure the safe design of advanced aero engines. The operating conditions of the compressor rotor–stator systems are characterized by small radial clearances, high relative tangential velocities, high airflow pressures, and elevated temperatures, which inevitably result in radial rubbing. This high-speed rubbing can damage both the stator coatings and rotor blades, and in extreme cases, lead to serious safety incidents such as "titanium fires " in aero engines. This paper presents a systematic review of research findings pertaining to high-speed friction and wear in rotor–stator interactions, focusing on the mechanisms of friction-induced wear and the associated heat generation. On one hand, the high-speed friction between compressor rotors and stators is influenced by various operational parameters such as intrusion rate, sliding velocity, and contact depth. On the other hand, factors inherent to the rubbing surfaces, such as blade thickness, coating hardness, and material thermophysical properties, also play a crucial role in determining the rubbing behaviors and mechanisms. The predominant wear mechanisms include adhesive wear, abrasive wear, oxidative wear, and several wear maps have been established. Among the operational parameters, intrusion rate and rubbing velocity have the greatest influence. In addition to the typical stator coatings, several new coatings for both the rotor and the stator have been proposed, and corresponding friction and wear mechanisms have been investigated under laboratory conditions. Accurate prediction of the increase in temperature is critical for addressing the heat generation during high-speed friction. A major challenge lies in determining the heat flow distribution; in this regard, various calculation methods have been developed based on fundamental assumptions. These methods provide a theoretical basis for estimating the increase in temperature. After determining the heat flow distribution, a thermal–structural coupled model can be established using finite element analysis to calculate the temperature increase. Experimental results can be used to refine the model and improve the calculation reliability. Moreover, molecular dynamic simulation provides a novel approach to calculate friction heat distribution and flash temperature, without requiring the use of the currently used heat partition coefficients. The heat generated during high-speed friction significantly affects the wear behaviors and mechanism, which is the focus of current studies. However, variations in wear mechanisms may also influence the friction heat generation and partition, especially when tribo-films or tribo-layers with distinct thermal properties from those of the original materials are formed on the surface. By controlling the operational conditions and designing friction interfaces, the generation, distribution, and dissipation of frictional heat can be altered and controlled, thereby reducing the friction and wear produced and, most importantly, the probability of titanium fires. Previous research has revealed friction wear mechanisms and the influence of friction heat under the action of multiple factors, providing theoretical guidance and a basis for engine structural design and coating development. Further studies should focus on novel coating–metal material combinations and explore the effects of additional operational conditions, as well as the influence of complex high-temperature, high-pressure, and high-velocity flows. Moreover, the effects of heat–solid–flow coupling and flash temperature on the friction, wear mechanism, and energy dissipation mechanism should also be considered to effectively address complex problems such as titanium fires. This review provides meaningful guidance for frictional heat calculation, comprehensive analysis of the friction and wear mechanisms of the rotor–stator systems, and development of novel coatings.

Electromagnetic launch technologies can directly convert electromagnetic energy into the instantaneous kinetic energy required for launching a payload within a short period. This technology has the advantages of high speed, high safety performance, and strong controllability, offering broad prospects for applications. Unlike mechanical and chemical energy, electromagnetic rail launch technology harnesses electromagnetic energy, enabling the achievement of ultrahigh launch velocities exceeding 2 km/s. During an electromagnetic launching process, a system is subjected to extreme launching conditions, such as high currents (~MA level), strong magnetic fields (~T level), high heat (~10³ K), and strong forces (~10⁶ N). Electrical energy is transformed into kinetic energy through an armature, making it a critical component of the launch system. However, the armature inevitably undergoes a series of damage during its operational lifespan, leading to significant changes in the contact characteristics between the armature and rail current-carrying friction pairs. This significantly affects the efficiency and precision of the electromagnetic rail launch system. This paper summarizes recent research progress on the surface damage mechanism and protection of armatures for electromagnetic rail launches, including typical damage characteristics and their influencing factors, a simulation and trend analysis of typical damage mechanisms, and the optimization of armature damage protection. Three primary forms of armature damage have been identified in various studies: current-carrying friction and wear, thermal melting, and transition erosion. The categories of current-carrying friction and wear encompass mechanical, current, and arc wear, presenting a distinct "three-stage" damage progression, correlating with the changes in current during the launch process. Thermal melting occurs owing to the contact resistance and friction between the armature and rails, which generate Joule and frictional heat, ultimately causing the armature surface to melt. Transition erosion manifests as a change in the contact mode between the armature and rails, leading to phenomena such as contact loss, which exacerbate the erosion on the armature surface and intensify the thermal melting damage. The severity and morphology of armature damage are influenced by service variables, inherent armature parameters, and their interplay. Simulations of armature damage mechanisms, conducted using finite element analysis software such as ANSYS, ABAQUS, and COMSOL, primarily focused on three aspects: the concentration of contact stress, current density, and heat. The optimization of armature damage protection requires considering various factors such as the structural designs of the armature and rail current-carrying friction substructure, material selection, and surface coating. These considerations aim to mitigate or prevent armature damage during launch. Existing studies have highlighted Al-Zn-Mg-Cu alloy as one of the most preferred materials for armatures, particularly when applies as a coating for surface protection. Currently, the preparation process, application conditions, and micro-mechanism of aluminum alloy armature coatings are not mature enough, especially in the extreme service environment of the launch process, which has a variety of coupled fields of physical quantities. Surface coatings with various impact resistances and other physical properties can meet the relevant standards, but systematic guidance is still lacking. Finally, a summary and outlook regarding the armature surface damage and protection are presented. The lack of a systematic and complete spatiotemporal evolution law in the morphological study of armature surface damage is attributed to the extreme harshness and multi-field coupling characteristics of the electromagnetic rail-launching armature surface damage formation. Further research is required for theoretical analysis, experimental validation of simulation reproduction methods, and correlation with rail damage characteristics. Future research should focus on the profound coupling of multiphysical fields, dynamic evolution of contact states between the armature and rail, development of three-dimensional analysis models under harsh operating conditions and material property evolution, and development of novel materials and structures for both the armature and rail. This study aims to enhance armature efficiency by incorporating insights from research on armature surface damage and protection, the development of new armature materials, and structural design improvements.

As an important supporting structure in wind power equipment, the tower plays a key role in supporting the continuous work of the motor and blades. However, the security risks, maintenance and renewal costs of the tower surface can increase sharply because of corrosion and wear. Organic coatings have been regarded as the most economical and convenient means by which to protect towers from corrosion. Among various coatings, waterborne epoxy resin coating is widely used because it is inexpensive and environmentally friendly. However, micropores and microcracks are usually generated due to the solvent evaporation process, which presents both a path for corrosion medium diffusion and a source of crack initiation and propagation. To address the above issue, various fillers have been introduced into waterborne epoxy resin coating to enhance its comprehensive properties. Among fibrous materials, basalt fiber has several excellent physical and chemical properties, such as excellent chemical stability, radiation resistance, mechanical properties, and low cost. Moreover, its preparation process is less harmful to the environment, and it is a veritable green material. However, adding basalt fibers into epoxy resin coating could lead to the formation of microdefects at the interface between the fibers and the coating due to their large size. Therefore, it is necessary to regulate the surface state of basalt fiber to resolve the incompatibility between the basalt fiber and coating. Hence, in this work, composite fibers (PU@BF) were prepared via in-situ polymer growth technology on the surface of basalt fibers by utilizing the structural and property advantages of polyurea nanofibers (PU) and basalt fibers (BF). Then, PU@BF was introduced into waterborne epoxy resin coating (EP) to prepare a fiber-based composite coating, and the tribological properties and corrosion resistance performance were investigated in depth. The scanning electron microscope results indicated that basalt fibers were uniformly covered by polyurea. The storage modulus values of all composite coatings showed a decreasing trend with increasing temperature, as increasing temperature leads to the accelerated movement of chemical bond chain segments as well as polymer segments. Hence, the coating gradually transitions from a highly elastic state to a viscous state. The storage moduli of EP, PU, BF, and PU@BF at 40 ℃ were 1 445, 1 460, 1 688, and 1 526 MPa, respectively, indicating that the mechanical performance of the composite coating was improved via the introduction of fibers. The friction factor of PU@BF was kept between 0.1–0.2, whereas that of EP was approximately 0.8, demonstrating that the introduced composite fibers had a great antifriction effect. The wear rate of PU@BF was 1.2×10^?5 mm³ / (N·m), which was decreased by about 78% compared with that of EP (5.5×10^?5 mm³ / (N·m)). The Rc value of PU@BF was 2.5 MΩ·cm² , whereas that of EP was 0.08 MΩ·cm² , indicating that PU@BF displayed better anticorrosion performance. Neutral salt spray test results showed that black-gray corrosive pitting was observed on the surface of an Al substrate only after 1 week of test, and the corrosion degree was increased after 3 weeks. However, the surface of an Al substrate of PU@BF was still bright and clean without corrosion, indicating that PU@BF had excellent protection performance. The enhanced antiwear / corrosion performance of PU@BF could be attributed to two reasons. First, the polyurea on the surface of the basalt fiber could reduce the microdefects between basalt fibers and epoxy resin to enhance the interfacial adhesion with epoxy molecules and thereby delay the diffusion of corrosion media during immersion. Second, the surface composite fiber layer can bear the vertical pressure and radial cutting force of the friction pair when the composite is subjected to a reciprocating force, and the inner composite fibers can reduce the deformation of the epoxy by exerting a pinning effect and thereby restricting the initiation and propagation of microcracks during friction. This research verifies the feasibility of a fiber / epoxy composite system to solve the “wear and corrosion” problem of waterborne epoxy coating. The results lay a foundation for the further optimization of the fiber / epoxy composite coating preparation process by exploring the influence law of the fiber orientation distribution on the comprehensive performance of a composite coating and its strengthening mechanism.

Ni-based alloys exhibit low density, good plasticity, high strength, and excellent corrosion and wear resistance under high-temperature conditions. Therefore, they are often preferred in high-temperature and harsh environments. They are widely used in various military engines and civil equipment fields such as thermal power generation, petrochemicals, and metallurgical industries. However, they are more prone to fatigue and creep damage in high-temperature environments, which seriously affect the working efficiency, reliability, and durability of equipment utilizing Ni-based alloys. To improve the service life of Ni-based alloys in harsh environments, NiCoCrTaAl-TiC composite powders were prepared via vacuum-mixed ball milling, and metal/ceramic composite coatings were successfully deposited on the surface of K418 nickel-based alloys via laser cladding technology. The phase compositions and microstructures of the coatings were examined using an X-ray diffractometer and metallographic microscope. The effects of different Al contents (0, 5, 10, and 15% ) on the mechanical and tribological properties of the NiCoCrTaAl-TiC composite coatings were examined using a micro-Vickers hardness tester, scanning electron microscope, high-speed reciprocating friction and wear tester, and ultra-depth-of-field microscope. Actual operating environments, such as rainwater environment (pH6.2), seawater immersion (pH8), and lubricating oil were simulated for the coating with the best wear resistance, and the corrosion and wear resistances of the coating in different environments were further examined. The results show that the composite coating is mainly composed of TiC, Cr₂Ni₃, Al₂O₃, and AlNi₃ phases, and intermetallic compounds such as Al₄CrNi₁₅ and Al₄Ni₁₅Ta. The internal structure of the coating is dense and composed of dendrites in the middle and equiaxed grains at the top. As the Al content increases, the average hardness of the coating initially decreases and then increases. The strengthening mechanism of the hardness corresponds mainly to the joint strengthening of TiC, Al₂O₃, and AlNi₃ phases. Under dry friction conditions, with increasing Al content, the wear loss of the coating initially increases and then decreases. Furthermore, the main wear form changes from adhesive to abrasive wear. In summary, when the Al content is 15wt.%, the composite coating exhibits the best microhardness, microstructure, and tribological properties, and its wear resistance is approximately 25% higher than that of the coating with 0wt.% Al content. Subsequently, the 15wt.% Al composite coating was immersed in rainwater and seawater for 2 h, and its friction coefficient was: lubricating oil ＜ rainwater ＜ seawater. The depth of the wear scar and amount of wear were essentially the same as those of the coating without corrosion treatment, indicating that the addition of Al can improve the corrosion resistance of the composite coating.

As the core component of metal-oxide arresters, ZnO varistors directly affect the insulation level of power equipment and the overvoltage level of the power system. ZnO varistors are crucial in suppressing overvoltage in power transmission and distribution systems. High-performance ZnO varistors are beneficial for improving the protection capability of the arrester, while affording lightweight and miniaturized equipment. Optimizing multivariate regulation technology and improving the sintering process are important for the development of high-performance ZnO varistors. However, the typical high-temperature sintering processes consume a significant amount of energy. To improve the energy-saving effect and comprehensive performance of ZnO varistors, the effects of different sintering temperatures (880, 930, 980, 1 030, 1 080 ℃) on the microstructure, electrical properties, and grain-boundary characteristic parameters of two types of ZnO varistors (ZB4 and ZB6) with a Bi / Sb ratio of 4∶1 are investigated in this study. The results show that the ZnO grains grow gradually as the sintering temperature increases. At the same sintering temperature, the liquid-phase amount of the ZB6-series samples is higher than that of the ZB4-series samples, which is beneficial to the distribution of the second phase around the ZnO grains. This corresponds to an improvement in the uniformity of the microstructure of the samples and an increase in the effective grain boundaries. The breakdown voltages of the ZB4- and ZB6-series samples are 329-1 074 V / mm and 429-1 161 V / mm, respectively. These breakdown voltages first increase and then decrease as the sintering temperature increases. In both the ZB4- and ZB6-series samples, the Bi / Sb ratio is 4∶1. The Bi₂O₃ contents in the ZB4 and ZB6 samples are 0.40mol.% and 0.60mol.%, respectively. At the same sintering temperature, the amount of Bi-rich phase in the ZB6-series sample increases, which is conducive to the integration of other metal oxides into the liquid phase. This improves the uniformity of the doping distribution and microstructure. By contrast, the formation of more Bi-rich phases, the incorporation of other metal oxides into the liquid phase, and the distribution of the liquid phase to the grain boundaries increase the number of grain boundaries formed and enhance the ability to increase the grain-boundary barrier height. At the same sintering temperature, an increase in the Bi-rich phase in the ZB6 sample improves the uniformity of its microstructure, thus resulting in a higher proportion of grain boundaries in the ZB6 sample than in the ZB4 sample. When the breakdown voltage increases, the corresponding grain-boundary barrier height increases as well. In general, the ZB6-series samples exhibit better nonlinearity and smaller leakage currents than the corresponding ZB4-series samples. At a sintering temperature of 930 ℃, the ZB4 and ZB6 samples achieve the best comprehensive electrical properties. The ZB4-930 sample (ZB4 sintered at 930 ℃) indicates a breakdown voltage of 1 074 V / mm, nonlinear coefficient of 6.58, leakage current of 101 μA, and grain-boundary barrier height of 2.42 eV. The ZB6-930 sample (ZB6 sintered at 930 ℃) demonstrates the best electrical performance, with a breakdown voltage of 1 161 V / mm, nonlinear coefficient of 13.22, leakage current of 24.5 μA, and grain-boundary barrier height of 2.97 eV. An appropriate Bi / Sb ratio is key to achieving low-temperature sintering for preparing ZnO varistor ceramics with excellent comprehensive performance. The results of this study provide an important experimental and theoretical basis for the development of high-performance ZnO varistors and the improvement of their energy-saving effects.

Line contact lubrication often suffers from oil starvation due to inadequate lubricant replenishment. Developing new replenishment strategies is essential for enhancing lubrication efficiency and extending the lifespan of components. This study presents an innovative lubrication replenishment technique by establishing oleophilic V-shaped array patterns on the surface using a chemical coating (AF) method. Via a lubricant film interferometry system, experiments were conducted to assess the impact of pattern length, orientation, and angle on oil film thickness under limited oil supply conditions in cylinder roller-glass disc line contact. The results reveal that the non-uniform wetting properties created by the oleophilic V-shaped array patterns facilitate the smooth flow of oil back to the center of the track, thereby improving oil supply at the inlet and increasing the lubricant film thickness. The pattern length influences the smoothness of lubricant flow from the sides to the center, with optimal lubrication achieved when the pattern width matches the track width. At high experimental speeds (u = 640 and 800 mm / s), the oil film thickness enhancement rates for a 1-μL oil supply reach 17.3% and 23.6%, respectively. However, a significant difference between the pattern width and lubrication track results in an increased time for the lubricant to return from the side ridges to the track, leading to insufficient replenishment at the inlet and worsening oil starvation. Fluorescence microscopy observations of oil pools at the inlet during backward and forward pattern movements reveal wave-like formations along the width of the roller. During backward movement, the V-shaped array (with the V opening facing the contact area) effectively reduces oil backflow and side leakage, significantly enhancing oil collection capacity at the inlet and increasing the amount of oil absorbed. By contrast, during forward movement, the V-shaped pattern accelerates oil diffusion to the sides of the track, resulting in lower oil film thickness than the original surface and exacerbating oil starvation. Further investigations using lubricants of varying viscosities show that as viscosity increases, oil starvation during forward movement becomes more pronounced, as higher viscosity hinders backflow. The study also examines the effect of pattern angles on oil film thickness and compares the oil film enhancement rates of the oleophilic V-shaped array pattern with spaced wetting patterns under similar conditions. The results indicate that the V-shaped wetting pattern exhibits higher oil film enhancement rates than spaced wetting patterns across different viscosity lubricants. For example, the oil film growth rates for the 120° V-shaped wetting array surface under PAO4, PAO8, and PAO20 are 109.298%, 187.335%, and 13.84%, respectively, whereas the 180° interlaced wetting surface shows film thickness enhancement rates of 58.79%, -1.74%, and -19.72%, respectively. This phenomenon becomes more evident as lubricant viscosity increases. The different film formation mechanisms between the two patterns likely contribute to these results. During backward movement, more oil accumulates in the geometrically reduced areas of the V-shaped pattern, creating additional pressure in the inlet oil pool and increasing oil absorption. However, during operation, some AF may transfer to adjacent hydrophilic areas on the 180° interlaced wetting surface, reducing surface energy and causing dewetting, which enhances oil film load-carrying capacity. The proposed method of employing chemically coated V-shaped array patterns to enhance lubrication is simpler, more efficient, and cost effective as compared with manufacturing techniques involving physical texturing. It provides a pathway for reducing wear and friction in line contact components and lays a research foundation for designing and applying geometrically patterned wetting surfaces in engineering.

Owing to their high melting point, strength, and hardness, ceramic coatings have been widely used as wear-resistant, corrosion-resistant, and thermal barrier coatings in fields such as aerospace, nuclear power generation, and weapon equipment. Plasma spraying is a highly promising surface cladding technology and has the advantages of a high heating temperature, high deposition rate, low substrate temperature, wide range of spraying materials, and low investment cost, making it one of the most widely used methods for preparing high-performance ceramic coatings. However, with the rapid development of the modern industry, critical equipment or components operating in extreme environments have higher requirements for the service performance of ceramic coatings. Therefore, improving the density and mechanical properties of plasma-sprayed ceramic coatings has become a popular research topic in this field. In recent decades, researchers worldwide have produced various high-performance dense ceramic coatings using optimized plasma spraying technology. Thus, summarizing the current research progress in this technology is highly significant owing to its large-scale promotion and application. First, the technical characteristics, microstructural features, and main issues of conventional atmospheric plasma spraying (APS) ceramic coatings are introduced from the aspects of the working principle and coating deposition process. Owing to the rapid energy dissipation and severe arc fluctuations associated with conventional APS technology, typical atmospheric plasma-sprayed ceramic coatings contain a large number of unmelted or semi-melted powder particles, as well as rich defect structures, such as large-scale pores and interlaminar cracks. This makes it difficult for the performance of ceramic coatings deposited by the conventional APS process to meet the requirements of industrial applications that require coatings with low porosity and mechanical properties, such as wear-resistant coatings, electrolytes of solid oxide fuel cells, and environmental barrier coatings. Subsequently, the structural design, working principle, and coating performance of eight plasma torch technologies for preparing dense ceramic coatings are systematically reviewed. By optimizing the electrode structure, powder feeding method, plasma jet protection, and heating method of the plasma torch, the operational stability, plasma jet energy output, powder heating, and acceleration efficiency of the plasma torch can be effectively improved. This is beneficial for preparing dense ceramic coatings with low porosity and excellent mechanical properties. Subsequently, the principles, process characteristics, and coating features of three typical high-efficiency plasma spraying processes for preparing dense ceramic coatings are elaborated in detail. By improving the operating pressure, plasma jet length, and powder injection method of the plasma spraying process, three dense ceramic coating plasma spraying processes, namely, very-low-pressure plasma spraying, long laminar plasma spraying, and suspension or solution precursor plasma spraying, are developed. These technologies effectively enhance the energy input and utilization efficiency of the plasma spraying process, significantly improving the heating and acceleration performance of refractory ceramic particles in the plasma jet, and are successfully applied in the preparation of various types of high-performance dense ceramic coatings. Finally, the development status of plasma-sprayed dense ceramic coating technology is summarized, and future development trends are discussed. This paper systematically summarizes the plasma torch technology and plasma spraying process used for preparing dense ceramic coatings, and is expected to provide a reference and guidance for the widespread application of plasma-sprayed dense ceramic coating technology.

Laser cladding is a three-way dynamic laser–powder–substrate interaction process in which the complex heat and mass transfer and convective behavior of the molten pool are closely related to the coating quality. Presently, it is difficult to visually and accurately observe the effect of the transient evolution of the laser cladding process on the coating quality by relying only on experimental methods, and it is limited by the high requirements of specialized equipment, high experimental costs, long cycle time, and other problems, which make it difficult to track the dynamic changes of multi-physical fields in the laser cladding process in real time. With the remarkable development of computer technology, numerical simulation provides an effective method for the in-depth analysis of the temperature change law, residual stress distribution, and melt pool flow behavior in the cladding process and provides a theoretical basis for process optimization and improvement of the coating quality. However, only a few reviews have addressed this aspect. Based on this, this paper reviews the current research status of the numerical simulation of multi-physical fields of the “temperature field–stress field–flow field” from the heat source models, thermal properties of materials, mechanical models and thermal-force coupling methods, as well as the flow behavior of the molten pool. The temperature and flow field evolution affect heat transfer, convection, and solidification in the molten pool, which directly affects the coating quality. Owing to the strong transient nature of laser cladding, stress is easily generated inside the coating, which affects its morphology, dimensions, and performance. However, current research on the numerical simulation of the laser cladding process is still limited in the accurate reflection of the actual cladding situation. In the future, it will be necessary to comprehensively consider the details of multiple physicochemical changes in the laser cladding process, such as phase transition, heat conduction, and heat convection, and build more reliable and accurate models to predict the properties of the cladding layer by considering heat source models and boundary conditions that are more compatible with laser cladding and by reducing model simplification. For the crack regulation problem, the influencing factors causing cracks are summarized. Cracks are mainly caused by residual stress exceeding the tensile strength of the material, while differences in the material properties, dilution rate, and elemental segregation also have an impact. The intrinsic correlation between multi-physics field-coupled dynamic evolution, process optimization, and crack regulation is also outlined. Numerous influencing factors lead to crack generation, and accurate simulation results are necessary to effectively guide practice. Therefore, the difficulties affecting the accuracy of the simulation are summarized, and an outlook is provided. In the future, we can improve the simulation methods, optimize the process and material systems, and combine them with nondestructive testing technology. Comprehensive simulation, experiments, monitoring, and other measures are used to establish a systematic and comprehensive crack quantitative index. Starting from the dynamic evolution level of multiscale multi-physical field coupling, realizing the integrated regulation of cracks will be the focus of future research. With continuous development and improvement at the industrial level, the realization of industrial intelligence and automation is an inevitable trend for future development, and the use of numerical simulation technology to guide the actual laser cladding process is a reliable method for effectively improving the coating quality. Therefore, a systematic review of the intrinsic connection between the dynamic evolution of multi-physics fields in laser cladding and crack regulation is necessary to provide references for subsequent research or practical work on numerical simulation and crack regulation of the laser cladding process.

Frictional wear occurs primarily on the surface of materials, and the failure of most mechanical components is due to the resulting surface wear, which not only reduces their reliability and safety, but is typically unavoidable in most mechanical systems with moving parts. The durability and reliability of engineering components are closely related to their wear resistance. The development of advanced materials to reduce the energy and material losses in moving mechanical systems remains a significant challenge. Novel high-entropy alloys composed of multiple principal elements offer promising prospects for the development of materials with excellent wear resistance owing to their superior hardness, outstanding wear resistance, and excellent corrosion resistance. However, the preparation cost of block high-entropy alloys is high, and high-entropy alloy films are difficult to apply in practical situations. Therefore, high-entropy alloy coatings have become a popular research topic. By preparing high-entropy alloy coatings on the surface of materials, the surface hardness, mechanical properties, friction, and wear properties can be significantly improved, thus extending the service life. High-entropy alloy coatings have shown enormous potential for applications in areas where the wear resistance of the base material is more demanding; however, there are few relevant review papers. Hence, it is necessary to review current research results on the wear resistance of high-entropy alloy coatings. It is imperative to review the current research results on the wear resistance of high-entropy alloy coatings. Additionally, it is of utmost significance to understand the research progress in improving the wear resistance of high-entropy alloy coatings and to facilitate their applications in industry. According to the materials science and engineering tetrahedron, it can be concluded that the microstructure, heat treatment method, temperature, cooling method, holding time, preparation process, processing process, and whether a protective oxide layer is produced during the friction and wear experiments contribute to a significant impact on the tribological properties of high-entropy alloy coatings. Nevertheless, alloy composition is a fundamental factor affecting the wear resistance of high-entropy alloy coatings. Therefore, this paper reviews existing research and summarizes the effects of metallic elements such as Al, Ti, Cu, Co, Nb, Mo, and W; non-metallic elements such as Si, B, C, and O; composite effects of elements; and ceramic particles such as TiC and WC on the microstructure, hardness, and abrasion resistance of high-entropy alloy coatings. The results showed that the microstructure of high-entropy alloy coatings and their strengthening mechanisms could be changed by a trace or a substantial number of alloying components, which in turn improves their wear resistance. Alloying is an effective way to improve the tribological properties of high-entropy alloy coatings. An appropriate alloying composition will not only lead to lattice distortion and solid solution strengthening of the coatings, but also generate hard phases, thus elevating their hardness and wear resistance. The lubrication mechanism of precipitation hardening and reinforcement doping into high-entropy alloy coatings originates from the formation of hard reinforcement phases during the preparation process. Although the wear resistance of high-entropy alloy coatings is linearly related to their hardness, the hard phase can also function as abrasive particles to accelerate damage to the wear surface and reduce the wear resistance of the base material when the hard phase is exfoliated. Accordingly, it is crucial to rationally adjust the type and content of the reinforcing phase. The challenges faced in the current research work are highlighted, and the application prospects and development directions of high-entropy alloy coatings are envisioned. It has a positive effect on the development of more scientific and reasonable wear-resistant design schemes, enhancement of coating durability, and practical application effects to systematically review the current research related to the influence of alloy composition on the wear resistance of high-entropy alloy coatings. In addition, it contains reference values for scholars and researchers in related fields.

Traditional hard coatings are typically prepared on the surfaces of crankshafts, shingles, and other friction parts to improve wear resistance. However, these coatings have been shown to have no wear-reducing effect on their counterparts, and the overall wear-reducing effect is poor. In this study, Fe / Ti₃SiC₂ wear-resistant and friction-reducing composite coatings were prepared on the surfaces of specimens of 45 steel using high-speed laser cladding technology under different process parameters. The objective was to achieve a friction vice that improves the wear resistance of the workpiece and reduces the wear of dyadic parts. The hardness of the composite coatings was examined under different process parameters using a Vickers microhardness test. Friction wear tests of the composite coatings under different process parameters were conducted at room temperature using a friction wear machine, and the wear mark morphology was characterized by scanning electron microscopy. Elemental analysis of some specimen areas was performed using self-contained energy dispersive spectroscopy. The wear amount of each coating on the pin of the grinding specimen was recorded as a criterion, and the mean value and extreme deviation of each process parameter were calculated to optimize the process parameters of the high-speed laser melting of the Fe / Ti₃SiC₂ wear-resistant and friction-reducing composite coatings. X-ray diffraction and optical microscopy were utilized to examine the physical phases and cross-sectional morphology of the composite coatings under different process parameters, and the effects of these process parameters on the organization and properties of the coatings were investigated.The optimal combination of process parameters for the composite coatings was estimated to be a laser power of 2.5 kW, powder feeding amount of 15 g / min, scanning rate of 14 mm / s, and coating microhardness of 591.7 HV_0.2. The macroscopic morphology of the cross-section of the single-pass cladding layer of the coating in the laser power was constant. When the scanning rate was too fast or the amount of powder delivery was too large, the dilution rate of the coating decreased whereby the coating showed an morphology, which in turn prevented the coating and substrate from forming a good metallurgical bond. The combination of coating and substrate was mainly composed of columnar, dendritic, and planar crystals, but the size of the organizational structure of the coating changed under different process parameters. With an increase in laser power, the input heat increased and the degree of subcooling decreased such that the grains coarsened. With a suitable increase in the scanning rate and amount of powder delivery, the fusion layer of powder particles was subjected to a lower heat and the rate of subcooling increased, which led to a refinement of the grains. A 30-min friction wear test at room temperature and under a 30-N load showed that the composite coatings under different process parameters exhibited different abrasion patterns. By contrast, the composite coatings under the optimal process parameters showed the best friction performance, where the amounts of wear of the coating and paired parts were 0.4 and 0.7 mg, respectively. Compared with the amount of wear of the matrix of non-fusion-coated composite coatings under the same friction wear test parameters, the wear amount of the composite coating was reduced by 94%, whereas that of the couple was reduced by 65%. By contrast, the Fe-based coating without Ti₃SiC₂ under the same parameters did not reduce the wear amount on the couple despite an increase in abrasion resistance; the wear amount on the couple was increased due to its own hardness. These results showed that the addition of composite coatings under appropriate process parameters, greatly improving the wear resistance of the workpiece surface while reducing wear on the dual parts. Thus, the performance of the entire friction system was systematically improved under the high-performance wear-resistant friction-reducing composite coatings. This study solves the technical problem wherein traditional hard coatings, despite enhancing the wear resistance of the workpiece, increase the wear of the spouse parts.