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.

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.

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.

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.

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in China 2025” and the strategy of maritime power, traditional marine anti-fouling coating materials have gradually withdrawn from the historical stage and been replaced by new biomimetic and intelligent marine anti-fouling coating materials.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

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

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.

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.

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.

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.

WO₃-NiO-based electrochromic devices (ECDs), which can actively regulate visible and infrared (IR) light and offer outstanding energy-efficient performance, have been extensively investigated owing to their potential application in smart windows for energy-efficient buildings and light-modulated skylight glass for electric vehicles. However, the high cost and low production efficiency of ECDs severely restrict their large-scale application. Compared with the conventional ECD fabrication process, which involves stacking multiple films on a single glass substrate, the lamination process for assembling a WO₃–NiO ECD by laminating the individual components of glass / TCO / WO₃ and glass / TCO / NiO with a transparent adhesive electrolyte interlayer is gradually becoming mainstream for realizing low-cost, commercially viable, large-area ECDs. However, for the practical production and new application of large-area laminated devices, one must perform a systematic survey from the starting material to device assembly, including high-quality EC oxide targets for large-area sputtering deposition; sputtered EC films with a regulated composition, microstructure, high performance, and color; achieve large transparent adhesive electrolyte foils with high room-temperature ionic conductivity, temperature stability, and high adhesive strength; perform a large-area ECD lamination process in the existing commercialized facilities; realize curved-device fabrication; and achieve an energy-efficient device with neutral color in both tinted and bleached states. Hence, researchers have conducted a series of studies, and the progress is presented in this review. First, the requirements and preparation methods of WO₃ and NiO ceramic targets for large-scale production are presented. An appropriate level of electrical conductivity is required to satisfy middle-frequency sputtering, which is the most commonly used sputtering mode in commercialized films. The EC performance and W / O stoichiometric ratio of a WO₃ film sputtered using a ceramic target can be effectively adjusted by changing the sputtering power and gas pressure under pure Ar atmosphere. In this study, the deposition rate increases from 6.9 to 20.8 nm as the sputtering power increases from 100 to 250 W. Additionally, an 18-nm-thick amorphous tin-zinc-oxide film is used to shield the sputtered WO₃ film so that a room-temperature-deposited film with excellent cyclic stability can be achieved. A high content of niobium (Nb / (Nb+W) = 54.1 at.%) is introduced into the WO₃ matrix to realize a neutral-tinted color and a relatively lower IR absorption in the tinted state. In the NiO film, Li / Si co-doping followed by rapid thermal annealing can enhance the transmittance near the short-wavelength zone in the bleached state, the charge capacity, and the cyclic stability. Additionally, W / Zn co-doping enables a NiO EC film with superior performance to be achieved after tempering at 640 ℃. For the transparent adhesive electrolyte interlayer, a new strategy for significantly improving the ionic conductivity of polyvinyl-butyral (PVB) via a cross-linking reaction with 3-glycidoxypropyltrimethoxysilane (KH560) is established. The cross-linked PVB solid polymer electrolyte (SPE) with 10 wt.% KH560 exhibits a high room-temperature ionic conductivity (1.51 × 10^?4 S·cm^?1 ). Additionally, the prepared PVB-SPE exhibits comprehensive optical, mechanical, and thermal performances, including high visible transmittance (＞ 91%), relatively high adhesive strength (2.13 MPa), and superior thermal stability (up to 150 ℃). The WO₃-NiO ECDs with sizes of 5 cm × 5 cm to 30 cm × 30 cm can be assembled in a commercialized autoclave to realize perfect lamination using the PVB-SPE foil. The device can be operated stably at temperatures ranging from -20 ℃ to 80 ℃, thus underscoring the potential of the PVB-SPE for realizing commercially viable large-area ECDs. Additionally, an ECD is assembled using the WO₃ system with a high Nb doping content. The ECD has a neutral color (a* = 0.6; b* =-2.7) and presents a high energy efficiency in reducing the interior-space air temperature by approximately 4.3 ℃ in its fully tinted state.

Cavitation is a phenomenon of material damage under extreme conditions of localized high pressure and heat. It commonly occurs in pumps and other flow-through components and can severely limit the service life of these parts. Polyamideimide (PAI) coatings were originally developed to prevent cavitation erosion damage in steel components. However, because of their lightweight requirements in aerospace, they are now being used as light alloys that can withstand low temperatures. Notably, PAI coatings have high curing temperatures that exceed the withstanding temperatures of most lightweight alloys. Although the addition of epoxy resin (EP) is expected to significantly reduce the curing temperature of PAI, it may also alter its overall properties. The corresponding effect on cavitation erosion performance is currently unknown. To address this issue, we prepared pure PAI coatings (P-280) and EP-modified PAI coatings (P-200 and P-170) with varying PAI contents. Using an ultrasonic vibration-accelerated cavitation erosion test, we then compared the cavitation erosion performances of the samples. Through characterization using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and nanoindentation, we also analyzed the mechanical and thermal properties of the samples and their force / heat response behaviors under the effects of cavitation load and cavitation heat. This study investigated the mechanical and thermal properties of the samples and their force-and heat-response behaviors using three-dimensional optical shaping. The results indicated that the addition of EP could significantly reduce the curing temperature of PAI by 80–110 ℃. However, this reduction led to the destruction of the mechanical properties of the material, including its toughness, which decreased to 8.21, 5.50, and 3.18 mJ·m^?3 in P-280, P-200, and P-170, respectively. This occurred because of the reduction in rigid molecular chains, such as the imide and benzene rings. In P-280, P-200, P-170, the tensile strength decreased gradually from 114.11 to 75.52 and 70.74 MPa. This reduction in strength led to a decrease in the bearing capacity of the coating and increased fatigue cracking under cavitation load, resulting in the formation of a greater number of larger spalling pits. However, the addition of EP significantly degraded the thermal stability of PAI, making it susceptible to melting and decomposition under cavitation heat. The reductions in temperature corresponding to a 5% weight loss of the P-170, P-200, and P-280 samples after 30 min of cavitation erosion were 15.24%, 14.82%, and 9.05%, respectively. This further accelerated the degradation of the mechanical properties of the coating surface and the damage caused by cavitation erosion. In addition, the heat generated by cavitation erosion promoted pyrolysis and hydrolysis of the molecular chains. XPS results indicated a reduction in the oxygen content after 30 min of cavitation erosion. Specifically, P-280, P-200, and P-170 decreased by 0.67, 1.9, and as much as 3.33at.%, respectively. The breakage of the molecular chains further deteriorated the overall performance of the coatings. The SEM morphology of the P-170 flaking debris showed melting under the heat of cavitation and the subsequent condensation of water into spherical debris particles. After 30 min of accelerated cavitation erosion, the mass losses of P-200 and P-170 were 1.7 and 3.6 mg, respectively. These values were 2.1 and 4.5 times higher than that of P-280, respectively. Considering the curing temperature, overall performance, and cavitation resistance of the coating, P-200 was deemed more suitable for application on the surface of light alloy parts. This study provides guidelines for the research and development of PAI coatings based on its investigation of the relationship between the overall and cavitation performances of PAI coatings under different EP contents.

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.

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.

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.

High-speed train braking systems experience stick-slip vibrations during low-speed braking, particularly before new brake pads reach a stable wear stage. Stick-slip vibrations lead to the abnormal wear and fracture of the friction blocks, threatening train braking safety. Moreover, they produce significant braking noise, which impacts passenger comfort and the everyday lives of residents along the route as well as leads to numerous complaints. Therefore, an in-depth study of the stick-slip vibration mechanism of high-speed train braking systems and the development of effective suppression strategies are crucial for enhancing train safety and passenger comfort. Stick-slip vibration, a typical friction-induced phenomenon, is significantly influenced by interface contact characteristics. Researchers have focused on studying interface contact characteristics and suggested that controlling these characteristics may suppress stick-slip vibrations. Considering the role of the surface texture in improving tribological performance, a series of parallel microgrooved textures of varying quantities are designed on the surfaces of the friction blocks. Finite element simulations and experimental analyses are combined to assess the effectiveness of microgrooved surface textures in suppressing stick-slip vibrations during high-speed train braking. Initially, finite element simulations reveal the effects of the number of surface microgrooved textures of the friction block on the contact stress, wear depth, interface contact degree, and vibration characteristics. These results indicate that the surface-microgrooved textures extended the primary load-bearing area in the direction of the texture, increase the contact area, and achieve a more uniform distribution of the contact stress. As the number of surface-microgrooved textures increases, the degree of interface contact gradually improves, and the amplitude of the displacement and velocity of the friction blocks decreases, transitioning from complex motion to more regular motion. However, finite element analysis alone struggles to account for the effects of wear debris generation and flow during friction, changes in wear surface morphology, and system vibrations, resulting in an incomplete reflection of the interface control function of the microgrooved surface textures. Therefore, friction tests must be conducted to verify the actual effects of surface-microgrooved textures in suppressing stick-slip vibrations. The experimental results indicate that surface-microgrooved textures effectively suppress high-frequency irregular vibrations and reduce the intensity of stick-slip vibrations. An analysis of the contact behavior reveals that microgrooved surface textures increase the actual contact area between the brake disc and friction block and thus play a role in reducing wear and dispersing interface contact stress, thereby favoring a rapid transition to a stable wear state. In addition, the design of surface-microgrooved textures optimizes the flow of interface wear debris, thereby facilitating their easy detachment and ejection, maintaining stable fluctuations in the friction force, and further weakening the intensity of the stick-slip vibration. Consequently, enhancing the friction interface contact state is the key to diminishing the stick-slip vibration intensity, and the optimal interface contact degree and mild wear characteristics contribute significantly to this improvement. The conclusions drawn from this study underscore the significance of enhancing the friction interface contact state to reduce stick-slip vibration intensity. The optimal degree of interface contact and mild wear characteristics are key contributors to this improvement. This study demonstrates that surface-microgrooved textures on friction blocks hold significant potential for mitigating friction-induced stick-slip vibrations during the bedding-in phase. The innovation of this study lies in its comprehensive approach to addressing the stick-slip vibration problem in high-speed train braking systems. Integrating finite element simulations with experimental validation provides a thorough analysis of the effectiveness of surface microgrooved textures. The mechanism by which these textures suppress stick-slip vibrations is elucidated, and practical insights into the design and optimization of friction blocks for high-speed trains are offered.

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.

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.

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.

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

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

The relationship between remanufacturing engineering and modern Iron & Steel industry was described in this paper. Remanufacturing engineering, with advanced surface technology, design and management methods, made a continuous technical improvement on steel facilities, such as prolonging their life time and retirement period, improving the grade and added value, which was the important method to realize high-efficient and green-steel developing model. The application and development of surface technology, such as electroplating and spraying, on continuous casting mould and roll steel equipment were introduced. It was sure that remanufacturing steel facility products would receive excellent characteristics and good economic and social performance, relying on the surface technology.

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.

Hainan is a tropical monsoon island. The Wenchang area is in the easternmost part of the island and is characterized by climatic characteristics such as high temperatures, high humidities, high precipitation, high salt spray content, and tropical cyclone landfall. In a tropical marine environment, which is harsh and has high air chlorine ion content, the performance of stainless steel is crucial. Marine engineering equipment is the basis for developing marine resources. The harsh corrosive environment of the ocean entails very high requirements for the corrosion resistance and safety factor of marine engineering equipment materials. Stainless steel has excellent corrosion resistance and mechanical properties, making it suitable for application in marine engineering and the oil extraction industry. Wenchang coastal area in the South China Sea is characterized by high temperature, high humidity, and high salt content, resulting in the corrosion of major equipment and facilities. In this study, 304 and 316 stainless steel were exposed to the atmospheric environment of the Wenchang coastal area. The surface corrosion morphology and corrosion product composition structure of the stainless steel were analyzed using scanning electron microscopy and X-ray photoelectron spectroscopy after atmospheric exposure. Additionally, the corrosion loss of metal materials was calculated after different exposure times to study the corrosion behavior and mechanism. The results showed that the corrosion degree of stainless steel in the Wenchang coastal area is significantly more severe than that in the Xisha Reef. As exposure time increased, the surface corrosion coverage on the stainless steel samples increased, and the degree of corrosion deepened. The corrosion mechanism was the pitting of the passivation film, loss of the protective effect, increase in corrosion products, and thickening of the rust layer. The Wenchang coastal area in the wind corrosion of stainless steel under severe corrosion. Chloride ions through wind erosion, adhesion, and precipitation are the main causes of the corrosion of stainless steel. Owing to the presence of significantly more chloride ions in the Wenchang Binhai tropical area, the passivation layer of the stainless-steel surface corrosion caused by the service life and safety performance relative to other marine environments is significantly reduced, resulting in a significant impact. The corrosion products of 304 and 316 stainless steel were basically the same. Initially, the corrosion product was FeOOH at atmospheric exposure, which transformed into Fe₃O₄ and finally Fe₂O₃ after long-term exposure. However, the pitting depth of 316 stainless steel was shallower than that of 304 stainless steel: the average pitting depths of 304 stainless steel exposed to sunlight for 3, 6, and 12 months were 8.29 μm, 5.40 μm, and 6.76 μm, respectively. Those for 316 stainless steel exposed to sunlight for 3, 6, and 12 months are 2.77 μm, 4.85 μm, and 4.10 μm, respectively. The corrosion loss rates of 304 stainless steel exposed to sunlight for 3 months and 1 year were 0.0015 g/(cm²•a), and 0.000 5 g/(cm²·a), respectively. Those of 316 stainless steel were 0.001 1 g/(cm²·a), and 0.000 5 g/(cm²·a), respectively. Thus, the corrosion resistance of 316 stainless steel was better. The depth of the pitting decreased in the late atmospheric exposure, because the development of pitting corrosion was initially rapid after atmospheric exposure, and the development of the late atmospheric exposure was slow. The results of this study provide actual exposure data and mechanisms for the corrosion protection of 304 and 316 stainless steel in the coastal environment of the South China Sea.

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.

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.

The rapid advancement in national defense technology has escalated the demands on aviation equipment. The importance and prominence of gears, being fundamental components, has been steadily increasing. Nonetheless, the development of surface tribological properties for gear pairs remains a challenge. Focusing on the tribology and texture design of gear pair surfaces holds the promise of significantly enhancing their service performance and advancing the design of high-reliability and long-life aerospace gears. This study begins with an overview of the basic meshing characteristics of gear pairs and delves into how surface roughness impacts their performance. It has been discovered that diminishing surface roughness effectively contributes to wear resistance. For decades, the tribological design of gear surfaces has evolved toward achieving higher precision and smoother finishes, grounded in conventional mechanical design and tribology principles. Despite advancements in polishing techniques, the average roughness of aviation gear teeth surfaces has been capped at approximately 0.4 μm. Given the considerations for processing cost-effectiveness, endlessly minimizing surface roughness is impractical. Recent research has demonstrated that under conditions of either rolling or sliding friction, a smoother surface does not necessarily equate to superior wear resistance and friction reduction outcomes.
Then, the influences of surface texture on the tribological performance of gear pairs are discussed. Over the past few decades, researchers from both domestic and international spheres have conducted extensive studies on the surface texturing design of gear pairs. The formation of surface textures through various processes is presented, along with a detailed review of the current research on gear surface texture design, covering both experimental investigations and theoretical simulations. According to the literature available, the benefits of surface texturing on performance are outlined, primarily encompassing friction reduction, wear resistance, surface strengthening, vibration damping, and temperature mitigation effects.
Subsequently, advancements in the numerical calculation of gear elastic-fluid lubrication are introduced, summarizing the effects of surface texture and texturing on the elastic-fluid lubrication characteristics of gear pairs. The prevailing numerical simulation efforts related to gear pairs mainly address two factors: surface roughness and texture. Historically, simulations of elastic-fluid lubrication for gear pairs predominantly utilized the infinite-length wire contact model. However, recent research has gradually shifted from this non-linear-length wire contact model to finite-length models that more accurately reflect the real contact length under actual surface conditions and mixed lubrication conditions, acknowledging the limitations of real wire contact length. Surface texture represents the three-dimensional morphology on the tooth surface, making the two-dimensional infinite-length model inadequate for current research needs. Investigating how to extend the application of three-dimensional wire contact models to numerically simulate surface texture, considering surface roughness, is of significant interest.
Following this, a comparative analysis of various surface texturing processing technologies for gear surfaces is conducted. This includes examining the advantages and disadvantages of specialized processing techniques such as laser etching, mask electrolysis, and micro abrasive jet texturing. Finally, a summary and outlook of the surface texture design of gear surfaces are proposed, including the existing research gaps and future research directions. Current design approaches for the surface texturing of gear pairs involve theoretical simulation and experimental optimization. Although surface textures present clear benefits and potential for application, it is important to recognize the challenges in designing surface textures for high-speed aviation gears, which remain areas for further exploration. The efficacy of surface textures on tooth surfaces is intrinsically linked to their operational conditions. The primary challenges are twofold: the design of gear surface textures and advancement of gear manufacturing technologies. Surface textures are believed to significantly enhance tribological performance, offering innovative solutions for the design of high-reliability and long-life aviation gears. This approach is anticipated to bridge the research gap in this domain and broaden the future application of surface texturing.

Tribocorrosion is a material-degradation phenomenon resulting from interactive effects between wear and corrosion. For various marine equipment, their key metal motion systems are typically affected by the combined effect of mechanical wear and chemical corrosion under the harsh marine environment, which can directly limit their stability and safety. Thus, comprehensive investigations into tribocorrosion behavior is critical for the design of appropriate engineering materials under the marine environment. Advancing marine exploration and deep-sea development necessitates surface and coating techniques to ensure favorable anti-corrosion and anti-wear performances for moving mechanical components. Many conventional techniques have been used to prepare protective coatings, such as spraying, high-energy beam surface modification, and physical vapor deposition (PVD). Among the diverse developed protective coatings, those realized via PVD exhibit favorable properties, including high corrosion resistance and excellent mechanical performance, which can effectively protect precision moving components used in deep-sea or offshore mechanical systems; thus, they are one of the most effective strategies in this field. This article focuses primarily on the development of anti-tribocorrosion coatings achieved via PVD and technologies used in the marine environment, in addition to the main scientific and technical issues encountered in the field. First, the tribocorrosion performance of carbon-based, nitride-based, high-entropy alloy, and transition metal dichalcogenide coatings are introduced, and the role of components and multilayer/nano-multilayer/nanocomposite/gradient structures on their tribocorrosion performance and related failure mechanism are summarized. The multilayer interface in coatings achieved via PVD not only significantly improves their hardness by hindering dislocation movement but also improves their corrosion resistance by hindering the diffusion of H₂O, O₂, Cl^-, and Na⁺ corrosives. To evaluate the tribocorrosion performance of coatings, electrochemical and tribological tests are primarily conducted in early research; currently, tribocorrosion tests are performed using a tribometer equipped with a three-electrode electrochemical system. By adopting in-situ atomic force microscopy (AFM) and an AFM-based “image-wear-image” tribology method, researchers are currently investigating subnanoscale and nanoscale wear, the tribocorrosion phenomenon, as well as the oxide growth mechanism of metallic materials. For advanced synergistic wear-corrosion models, a novel two-dimensional predictive model has been developed for predicting the synergetic wear-corrosion reliability of Ni/GPL and steel. Additionally, a combined experimental and computational investigation has been performed using Al single crystals to develop a crystal-based tribocorrosion modeling framework that considers the effects of lattice reorientation and dislocations on surface corrosion. Additionally, new strategies that combine PVD with other surface-protection technologies have been developed, for example, duplex coating systems formed via the PVD of CrN or carbon-based coatings and thermal layer spraying using a high-velocity oxyfuel. Using these methods, material losses due to the synergistic effects of wear and corrosion can be reduced. In particular, hydrogenated carbon-based coatings present high tribocorrosion resistances under low loads due to their high hardness and excellent corrosion resistance; however, they exhibit catastrophic delamination under heavy loads, whereas hydrogen-free carbon-based coatings exhibit better tribocorrosion performance owing to their gradual shearing characteristic. Additionally, carbon-based coatings can enhance the anti-corrosion properties of microarc oxidation (MAO) coatings on magnesium alloys. The superior low-friction and anti-corrosion properties of carbon-based coatings/MAO render them preferable as protective coatings on magnesium alloys. Cr layers achieved via thermal diffusion metallization and CrN coatings deposited via PVD are used to strengthen the surface of 45 steel, thus improving its surface hardness and abrasion resistance. By implementing ion implantation and Al/AlN/CrAlN/CrN/MoS₂ gradient duplex coatings, both the anti-wear and anti-corrosion properties of AM60 magnesium alloy are improved. For AISI 4140 steel, plasma nitriding applied before the coating significantly improves the corrosion and tribocorrosion resistances of PVD CrN, TiN, and AlTiN coatings. Typical applications of anti-tribocorrosion coatings achieved via PVD include seawater-pump plungers, hydrostatic slipper bearings, ball valves, and components of a helicopter-cockpit instrument panel. Hydrogenated diamonds coated with Cr and WC as transition layers are prepared on the plunger of marine diesel engines. These coatings can significantly improve the hardness and elastic modulus while decreasing the friction factor under heavy-diesel-oil environments. After a bench test is performed, the wear marks on the surface of the plunger with coating are extremely narrow and shallow. For drill pump valves, implementing TiN coatings can increase their service life by three times. In the cockpit of a helicopter, multigradient nano-black coatings achieved via PVD are thin and the thickness tolerance is low; additionally, these coatings satisfy the requirements of the salt spray test. Finally, the development and application of anti-tribocorrosion coatings achieved via PVD under the marine environment are proposed. Machine-learning and big-data sharing services should be used to comprehensively understand the damage mechanism; the optimization and design of the suitable coating should account for the actual operating conditions, such as deep sea, nearshore, and shallow sea; advanced coating equipment should be developed for the inner wall of certain pipelines; and in-situ evaluations and bench experiments should be performed to evaluate the service life of metal mechanical components and coating materials. This review presents a comprehensive and systematic report pertaining to anti-tribocorrosion coatings achieved via PVD for marine applications.

Weight loss of Ni、n-Sic/Ni and n-Al₂O₃/Ni coatings after 96 hours corrosion in 5%H₂SO₄、5%H₂SO₄+3.5%NaCl are introduced，corrosion morphology and components are analyzed by SEM and X-Ray diffraction. The theories of corrosion coatings are discussed as well. The results show that micro-corrosion batteries are generated due to non-uniform coating structure．

From the point of view of Green Remanufacturing, the article has introduced servicing project and analyzing advantage what was achieved to apply the technology of Green Remanufacturing. It is great important and long-term, to economizing resource and protecting environment，to helping the harmonious development of army economy、society and environment.

Engine remanufacturing technological process service for the total request of engine remanufacturing, the performance and quality of remanufactured engine equal or exceed the new prototyte engine. The reused rate of core is the main standard to evaluate the contribution to cycle society. Adopt high-technology is the key process to improve the reuse rate. The base market operation mode of engine remanufacturing includes purchase core and sale remanufacturing engine by OEM, self-operate by remanufacturing company, self-operate or supporting supply by engine parts company.

Solid lubricating coatings represented by layered materials, such as graphite and molybdenum disulfide (MoS₂), have extremely low friction coefficients and wear rates and are currently considered superior lubricating materials in many fields. However, as a typical interfacial process, the performance of solid lubricants is largely dependent on environmental factors such as humidity. Due to the significant technical challenges encountered by experimental methods in real-time and in situ detection of the dynamic evolution process of friction interfaces, theoretical research plays an increasingly important role in revealing material lubrication behavior and mechanisms. Starting with classical friction analytical models, this paper reviews and summarizes commonly used atomic-level theoretical research methods, including classical molecular dynamics (MD) simulations, first-principles static potential energy surface (PES) calculations, and ab initio molecular dynamics (AIMD) simulations. Classical analytical models, such as the Prandtl-Tomlinson and Frenkel-Kontorova-Tomlinson models, are the foundations for understanding the friction behavior of materials. Although these models ignore many realistic factors of materials, they can clearly reflect the basic physical characteristics of friction, such as specific stick-slip and continuous low-dissipation sliding behaviors. Based on analytical models, a classical MD simulation is further introduced, which can better consider atomic details and further investigate the friction, adhesion, wear, and lubrication behaviors of materials. The accuracy of classical MD depends on the preset force field, and the simulation results are usually based on the material structure and morphology, such as the puckering effect and evolution of interface quality. However, due to the complexity of realistic environments, the friction process often involves many electronic interaction mechanisms that classical MD cannot handle, such as complex coupling behaviors among the substrate, lubricating film, and environmental substances. Density functional theory (DFT) calculation is suitable for revealing these electronic interaction mechanisms, as it can provide all the ground-state properties of materials by solving the electronic wavefunction. In friction research, DFT can be used to simulate the PES of sliding interfaces, reflect the difficulty of sliding, and reveal the electronic origin of PES fluctuations. Therefore, exploring the complex interactions between various environmental substances, material substrates, and defect sites as well as the effects of environmental substance adsorption, aggregation, and diffusion on the long-term stability of coatings is necessary. However, although static DFT calculations can accurately reveal the electronic interaction mechanism, they cannot consider the dynamic evolution process involved in friction, such as the dynamic disturbance of environmental water molecules and the internal stress generated by interface sliding. AIMD simulations are ideal in that they consider both electronic interactions and the dynamic evolution of friction. In addition to reviewing existing AIMD simulation models, this work introduces a new “slow growth” AIMD simulation method and conducts systematic verification calculations in representative MoS₂ systems, revealing the effectiveness and accuracy of the “slow growth” method in studying material friction behavior. Compared with classical MD, AIMD simulations have the problems of small scale and slow speed, which severely limit their application. With the development of artificial intelligence technology, machine-learning methods have been used to train MD force fields based on AIMD calculation data, opening the door to a comprehensive exploration of macroscopic engineering problems using computational simulations. Accordingly, this work introduces an “on the fly” machine-learning method, which can continuously train and improve the force field during the AIMD calculation process, greatly accelerating the calculation speed while ensuring the accuracy of the calculation to a certain extent. The summary and outlook of the theoretical simulation methods in this work can help to better understand the microscopic lubrication mechanism of materials in complex environments in the future and guide the design of advanced lubricating coatings.

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.

Mechanical seal is crucial for preventing medium leakage in rotating equipment and is widely used in the mechanical industry. Seal-interface friction damage is accelerated under certain conditions (e.g., high temperature, high speed, and start/stop-stage dry friction), which increases leakage, reduces lifetimes, and other problems that directly affect the service performance of key seal friction components. Diamond coatings deposited via chemical vapor deposition are the best sealing material for conventional ceramic seals owing to their excellent properties, which are similar to those of natural diamond, e.g., high hardness, low friction and wear resistance, high thermal conductivity, and high corrosion resistance. In this study, diamond coatings are deposited on SiC seal-ring and sheet substrates via hot-filament chemical vapor deposition (HFCVD). Microcrystalline diamond (MCD) and ultrafine nanocrystalline diamond (UNCD) coatings are applied to SiC ceramic seals. The friction of diamond-coated seals with different grain sizes is evaluated by a high-duty mechanical seal-ring evaluation equipment. The results show that the friction factor of the MCD is approximately 0.24, and the wear rate is 0.67×10^-6 mm³/(N·m), and the friction factor of the UNCD is approximately 0.22, and the wear rate is 3.43×10^-6 mm³/(N·m). The friction factor of the diamond-coated modified mechanical seal ring is 4 to 5 times lower than the conventional SiC ceramic seals, and the wear rate is about 20 times lower than the conventional SiC ceramic seals. Compared with the UNCD coating, the MCD coating demonstrates higher adhesion and wear resistance in the same arid friction environment, albeit with a slightly higher factor of friction. Dry-friction test results of the mechanical seal ring show severe adhesive wear in the dry-friction process between SiC and SiC sealing rings, which contributed to the large friction factor and severe wear of SiC sealing rings. When the diamond-coated sealing ring is paired with the SiC sealing ring, adhesive wear is avoided owing to the high hardness of the diamond coating. The diamond-coated sealing ring is paired with a SiC sealing ring, which avoids adhesive wear due to the high hardness of the diamond coating, whereas low wear is achieved by sacrificing the softer SiC sealing ring during the dry-friction process. The low factor of friction of the UNCD is due to the low adhesion of the grains. When the frictional resistance is high, the frictional resistance can be reduced by reducing the larger obstructed grains; simultaneously, the contact surface is smoothed promptly and the surface roughness is reduced, thus resulting in a lower friction factor and a greater amount of wear. To investigate the effect of diamond coatings with different grain structures and surface roughness on dry-friction properties, grinding and polishing techniques are adopted to reduce the surface roughness of the diamond coatings, and X-ray diffraction (XRD) is performed to confirm that the grain structure does not change before and after grinding and polishing. The friction and wear properties of the MCD and UNCD diamond coatings after grinding and polishing are systematically evaluated by friction experiments. The results show that the factor of friction of the MCD coating improved significantly by refining the surface roughness via grinding and polishing, and that the factor of friction is consistent with that of the stable UNCD measurement, i.e., 0.07. Additionally, the wear rate of silicon-carbide balls decreases from 3.21×10^-6 to 0.09×10^-9 mm³/(N·m), which is attributed to the optimization of surface roughness during dry friction and improved MCD effects after abrasive and adhesive wear, which effectively broadens the utilization range of MCD as a defensive coating for mechanical seals.

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.

Thermal barrier coating technology, an internationally recognized cutting-edge technology for heavy-duty gas turbine manufacturing, is mainly used on the surface of the hot section components of gas turbines to enhance their efficiency by increasing the working temperature of the hot section components. However, at high temperatures, thermal barrier coatings frequently experience issues including CMAS (CaO-MgO-Al₂O₃-SiO₂) corrosion, oxidation, phase transitions, and sintering. Key properties such as CMAS corrosion resistance affect the coating life, which affects the efficiency of gas turbines. Therefore, this paper first presents the current situation and development trends of heavy-duty gas turbines worldwide. The background of the research on thermal barrier coatings is then presented; thermal barrier coatings are classified according to their different coating structures. The characteristics and properties of commonly used coating materials such as the ceramic top coat and bond coat materials are compared, and the principles, advantages and disadvantages of several typical preparation processes of thermal barrier coatings such as air plasma spraying, electron beam-physical vapor deposition, plasma spraying-physical vapor deposition, and the morphological characteristics of the prepared coatings are summarized and analyzed. Aiming at some challenges that are often encountered in thermal barrier coatings for gas turbines at high temperatures, such as oxidation, CMAS corrosion, among others, the importance of several key properties of thermal barrier coatings, such as thermal insulation, oxidation resistance, and thermal shock resistance, is emphasized, and these key properties are explained and their research progress is reviewed. Finally, focusing on the high-temperature CMAS corrosion resistance of thermal barrier coatings, the mechanism of CMAS corrosion in terms of the thermochemical and thermomechanical aspects is described, along with five protective research methods to improve the CMAS corrosion resistance of thermal barrier coatings: identifying and developing new ceramic top coat materials, doping and modifying thermal barrier coating materials, preparing a protective layer on the surface of the ceramic top coat, adopting a double-layer ceramic top coat structure, and optimizing the coating surface structure. Based on a summary of the research progress and development trends of heavy-duty gas turbines and their thermal barrier coating, the following conclusions are drawn. Compared with developed countries, there is still a wide gap in the manufacturing technology and maintenance level of heavy-duty gas turbines in China, which will be developed towards high parameters, high performance, low pollution, and large-scale in the future. In general, the thermal barrier coating is preferred in the form of a double-layer structure; the material is preferred to be 8YSZ and MCrAlY, and the preparation process is preferred for air plasma spraying. Despite the fact that thermal barrier coatings have been widely used with the rapid development of industry, traditional thermal barrier coatings have failed to meet the service requirements of next-generation heavy-duty gas turbines; therefore, improving the performance of thermal barrier coatings has become a key issue. The materials, structures, and preparation processes of thermal barrier coatings are critical for improving their performance. To ensure the safe operation of heavy-duty gas turbines at higher temperatures for a longer period of time, we should continue to search, design, and develop new thermal barrier coating materials with low thermal conductivity, good oxidation resistance, thermal shock resistance, and corrosion resistance, increase investments in the structural design research of thermal barrier coatings, regulate the structural parameters of thermal barrier coatings, and improve and develop new preparation processes for thermal barrier coatings. This paper reviews several key properties of thermal barrier coatings for gas turbines and proposes that the performance of thermal barrier coatings is closely related to their materials, structures, and preparation processes. Methods to improve the performance of thermal barrier coatings are presented, and there is a lack of such review articles to lead the field of thermal barrier coatings for gas turbines.

Environmental pollution has become an increasingly serious issue. Numerous studies have revealed that the increased incidence of cancer and other diseases can be associated with environmental pollution. Pollutants include not only inorganic matter, but also bacteria and organic matter. Photocatalytic breakdown of contaminants in the environment is considered an ideal cleaning technology, and one of the most promising photocatalytic compounds is titanium dioxide (TiO₂). However, their utilization efficiency and range are limited because of their narrow energy bandwidth and the quick recombination of photogenerated electrons and holes. Therefore, developing efficient TiO₂-based photocatalytic composites is crucial. A simple sol-gel and one-step Marangoni methods were used to efficiently combine TiO₂, Ag nanoparticles (AgNPs), and graphene oxide (GO) to make composites of TiO₂@Ag-GO with significantly enhanced photocatalytic activity and antibacterial capabilities. GO has multiple catalytically active centers that can efficiently degrade pollutants via photocatalytic reactions. Simultaneously, it can improve charge separation, restrict the recombination of photogenerated electrons and holes, and boost the photocatalytic activity of TiO₂. AgNPs can hold electrons, facilitate charge separation, and release Ag⁺ , making them a material with diverse antibacterial properties. Ag-doped TiO₂ sol-gel was prepared by the sol-gel method, and the prepared sol-gel was then coated on the surface of an Si substrate via spin-coating. An anatase-type Ag-doped TiO₂ film (TiO₂@Ag) was prepared via heat treatment. Finally, the TiO₂@Ag-GO nanocomposite photocatalytic material was effectively prepared by transferring a large-area ultrathin GO film, produced via the single-step Marangoni process, onto its surface. The compositions of the films made of TiO₂ and TiO₂@Ag were examined using X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Photoelectron Spectroscopy (XPS). the Ag in the TiO₂@Ag sample was primarily in the form of Ag2O nanoparticles, and the TiO₂ sample was primarily composed of anatase crystals. Ion-release experiments demonstrated that TiO₂@Ag-GO could stably release Ag⁺ from Phosphate Buffered Saline (PBS) for at least 12 d. The rates of TiO₂ and TiO₂@Ag degradation in a 2 h photocatalytic methylene blue degradation test were 42.4 and 52.5%, respectively. Simultaneously, the degradation rate increased considerably after the addition of GO, reaching 74.5% for TiO₂@Ag-GO. These findings suggest that Ag doping and GO loading enhance the photocatalytic activity of TiO₂. This is because when TiO₂ is modified by AgNPs and GO, TiO₂ absorbs UV radiation; the electrons generated by TiO₂ are transferred to the AgNPs, which demonstrate electron storage capability, serving as electron traps that promote charge separation. In contrast, GO on the semiconductor surface contains numerous catalytically active centers that can efficiently break down pollutants in a photocatalytic reaction. Furthermore, GO significantly enhances photocatalysis by increasing the degree of charge separation and preventing the recombination of photogenerated electrons and holes in the semiconductor. Seeding assays with Gram-negative (Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus) were used to assess the broad-spectrum antibacterial capabilities of the composites. Scanning Electron Microscope (SEM) images and statistical analyses of bacterial adhesion and proliferation revealed that many bacteria attached to and proliferated on the TiO₂ surface, and the bacteria tended to aggregate to form colonies. The wrinkled shape of the GO surface prevented bacterial aggregation, resulting in a more even distribution of the bacteria on the TiO₂-GO surface, with significantly fewer bacteria present. The TiO₂@Ag and TiO₂@Ag-GO surfaces drastically reduced the number of bacteria and severely damaged their morphology, demonstrating significant bactericidal activity. AgNPs and Ag⁺ can bind to negatively charged bacterial biofilms, disrupting the bacterial membrane potential, and leading to bacterial death. This simple TiO₂-based composite, with significant photocatalytic and antibacterial activities, has considerable potential for use in photocatalytic cleaning.