The failure of metallic materials often originates from their surface. Surface strengthening technology can effectively extend the service life and improve the working efficiency of metal components. High-entropy alloy coatings exhibit significant advantages of uniform composition, dense structure and stable structure through the size effect induced by their unique low-dimensional forms(such as films or nanoparticles), which synergizes with their multi-principal component characteristics. The size effect effectively enhances the overall performance of coatings by influencing their interfacial stress distribution, surface energy, and defect evolution. This paper systematically reviewed the primary fabrication techniques of high-entropy alloy coatings, thoroughly investigated their microstructural characteristics and service performance, and analyzed the intrinsic correlation mechanisms among composition, processing methods, microstructure and properties. Meanwhile, the application value of numerical simulations in coating preparation, microstructural evolution, and performance characterization was further elaborated, and perspectives were provided on future research directions and engineering applications of high-entropy alloy coatings. Generally, the study aimed to clarify the preparation pathways and performance evolution laws of high-entropy alloy coatings, reveal their strengthening mechanisms and the correlation between composition, processing and performance, explore the application of numerical simulation in coating design and optimization, and provide theoretical support for their engineering applications.

Bearings，regarded as the “heart” of aircraft engines，operate under extreme conditions involving high temperatures，high pressures，and high speeds，with fatigue being their primary failure mode.To enhance the performance of aerospace bearings and consequently improve the reliability and service life of aircraft engines，the application of surface strengthening technologies proves particularly crucial.Firstly，the primary failure modes of rolling contact fatigue in aerospace M50 bearing steel were reviewed based on the mechanisms of bearing failure，with subsurface-initiated rolling contact fatigue identified as the primary failure mode，and the causes of fatigue failure were subsequently discussed.Secondly，based on the severe plastic deformation mechanism，the strengthening modification effect of surface strengthening processes on the surface service performance of bearing steel was analyzed from the perspectives of grain deformation and stress strengthening.Through grain refinement and the introduction of residual compressive stress，the fatigue resistance of the material was significantly improved.Additionally，recent research progress on existing surface strengthening processes was summarized，including various methods such as ultrasonic rolling，shot peening and laser shock hardening.Finally，limitations of existing single-process approaches were identified，along with development directions for strengthening and modification processes specifically for M50 bearing steel.

In the service life of reinforced concrete structures，the corrosive medium enters the concrete and causes the corrosion of steel bars，and the corrosion products produce compressive stress on the surrounding concrete due to the volume expansion.This ultimately induces tensile stress in the concrete protective layer，causing cracking，which further affects the load-bearing capacity and service life of the concrete structure.Due to the characteristics of medium erosion，the chloride ion concentration on the side closer to the protective layer is higher than that on the side farther from it，resulting in non-uniform corrosion of steel bars.Therefore，it is of great significance to analyze the effects of non-uniform corrosion on the cracking of protective layers and the impact of the corrosion of steel bars on the durability of concrete through experiments and theoretical analysis.Based on existing research achievements both domestically and internationally，this paper provided a detailed review of current studies on concrete cracking induced by non-uniform corrosion from three key aspects:the obtained rust layer distribution model of steel bars，the rust expansion force model，and the rust expansion cracking model.Furthermore，the limitations of current research and future development trends were analyzed，aiming to provide reference for the study of concrete cracking caused by non-uniform corrosion of steel bars.

With the development of modern industry，the demand for lubrication in various working environments has become increasingly stringent.Conventional lubricants can no longer fully meet the performance requirements of mechanical operating conditions，making the development of new lubricants a critical research focus.To meet the requirements of comprehensive salt-lake resource utilization，two novel solid lubricant materials，organic amine-intercalated magnesium phosphate (MgP-18N) and organic amine-intercalated magnesium boron phosphate (BP-18N)，were prepared via a mixed solvothermal method.Their tribological properties as lithium-based grease additives were investigated using an oscillating ball-on-disc tribometer.Results showed that the optimal addition amounts of both MgP-18N and BP-18N in lithium-based grease were 3.0%.The addition of MgP-18N and BP-18N increased the extreme pressure load capacity of the lithium-based grease to 700 N and 800 N，respectively.Both MgP-18N and BP-18N demonstrated excellent high-temperature applicability.After treatment at 700 ℃，the samples maintained superior friction-reducing performance during a 10 h long-term tribological test under a 300 N load，with the friction coefficient consistently remaining at a low level (around 0.1) and with stable dynamic curves.Overall，BP-18N exhibited superior tribological performance.The morphology，elemental distribution and chemical states of the worn surfaces were analyzed using a three-dimensional (3D) optical profiler，scanning electron microscopy (SEM)，energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS).During the friction process，both MgP-18N and BP-18N readily adhered to the worn surfaces，forming lubricating protective films that effectively prevented direct contact between the surfaces of friction pairs.Notably，BP-18N underwent chemical reactions during friction，generating iron-boron compounds，boron oxides，and boron-nitrogen compounds，which significantly enhanced the tribological performance of lithium-based grease.

The inductively coupled plasma (ICP) etching technique，along with polystyrene (PS) microspheres as masks for etching technology，has been widely applied in the fabrication of silicon nanoarrays.However，the size reduction process of PS microspheres during etching is often accompanied by surface quality degradation.Additionally，the morphology of PS microspheres is influenced by multiple process parameters，making research challenging.To address these challenges，an orthogonal experimental method was employed to thoroughly investigate the process effects of the ICP process in the size reduction of PS microspheres with a particle size of 10 μm.Results showed that the gas composition had a significant impact on the etching effect，while the RF power exhibited positive correlations with both microsphere size reduction and surface roughness，pressure showed a negative correlation with microsphere surface roughness，and gas flow rate had negligible effects.Based on the above conclusions，the optimal process parameters were ultimately determined as follows:addition of 20%CF4 to O2，RF power 200 W-100 W (inductive power-DC bias power)，pressure 3.0 Pa，and gas flow rate 50 mL/min (O2 ∶CF4 flow ratio of 4 ∶1).Under the optimal process parameters，the surface roughness was minimized without compromising the etching reduction effect of PS microspheres.The highly linearized silicon nanoarrays with smooth outer surfaces were successfully fabricated using this optimized template.

Alloys with low Ti/Al content exhibit insufficient strength，while those with high Ti/Al content are prone to cracking during laser additive manufacturing.To achieve a balance between high γ′ phase volume fraction and low crack susceptibility，this study proposed an alloy design strategy: appropriately reducing Ti/Al content while increasing Ta content based on the high-Ti/Al IN738LC alloy.Based on this design strategy，the microstructures and properties of four laser additive as-deposited samples with different Ta contents before and after solid solution treatment and aging treatment were studied.Results showed that with increasing Ta content，the as-deposited samples exhibited grain refinement and a higher γ′ phase fraction.The tensile strength and yield strength of both as-deposited and heat-treated samples increased as the Ta content increased，while their ductility decreased and cracking susceptibility intensified.When the mass fraction of Ta in the heat-treated samples reached 5%，η-phase precipitation occurred.At 7%Ta content，excessive η-phase formation led to brittle fracture surfaces in tensile specimens.Moreover，the sample with 5%Ta exhibited an optimal strength-ductility combination: at 25 ℃，yield strength of 962 MPa，ultimate tensile strength of 1 212 MPa，and elongation of 11.0%；while at 900 ℃，yield strength of 410 MPa，ultimate tensile strength of 486 MPa，and elongation of 6.1%.Generally，through optimization of Al，Ti and Ta contents，this study successfully developed a γ′-phase strengthened laser additive manufactured nickel-based superalloy.The alloy achieved an optimal balance between high γ′-phase volume fraction and low cracking susceptibility，demonstrating excellent comprehensive mechanical properties，and these findings provided valuable insights for the compositional design of laser additive manufactured nickel-based superalloys.

Ti6Al4V titanium alloy is a commonly used material for components such as dovetail joints in aircraft，which must endure hightemperature service environments.In order to investigate the influence of micro-arc oxidation (MAO) on the fretting wear resistance of Ti6Al4V titanium alloy in the high-temperature range，oxide coatings were prepared on the surface of Ti6Al4V.The microstructure and phase composition of the MAO coatings were characterized using scanning electron microscopy (SEM) and X-ray diffractometer (XRD).Fretting wear tests were conducted at 300 ℃ to obtain the friction coefficient，wear profiles and microscopic wear damage morphology.Results showed that after MAO treatment，a coating with a thickness of about 10 μm formed on the surface of Ti6Al4V，containing hard Al2TiO5 and rutile TiO2 phases.Compared to untreated specimens，the MAO-treated samples exhibited lower friction coefficients and reduced wear volumes under various displacement conditions，demonstrating that MAO effectively improved the fretting friction and wear behavior of Ti6Al4V in the high-temperature range.Increased coating hardness was conducive to enhanced wear resistance.Additionally，under high-temperature conditions，dense TiO2 and Fe2O3 oxide films were more likely to form on the MAO-coated surface，providing protection to the substrate.Besides，the wear mechanism of the MAO coating was primarily delamination wear and abrasive wear，while the titanium alloy substrate mainly underwent fatigue wear and adhesive wear.

In order to solve the problem that the surface of silicon nitride ceramic bearings is susceptible to wear under extreme operating conditions，gradient，multilayer and monolayer TiN films were prepared on silicon nitride substrates using magnetron sputtering.Three nitrogen supply modes were implemented: a gradual increase starting at 15 mL/min with 0.8 mL/min increments every 5 min，an alternating on-off switching between 0 and 30 mL/min，and a constant 30 mL/min flow.The influence of film structure on surface morphology，cross-sectional morphology and microstructure was investigated using X-ray diffractometer (XRD) and scanning electron microscopy (SEM)，while the filmsubstrate adhesion and tribological properties were evaluated through scratch and friction-wear tests.Results showed that under identical testing conditions，the gradient TiN film exhibited the highest film-substrate adhesion strength (LC2 ＝19.12 N)，representing an approximately 30%improvement compared to the monolayer TiN film.Compared to silicon nitride’s friction coefficient (0.78) and wear rate [1.51×10－5 mm3/(m·N)]，both the friction coefficients and wear rates of TiN films with different film structures significantly decreased.Among them，the gradient TiN film exhibited the lowest friction coefficient (0.10) and the lowest wear rate [3.33×10－6 mm3/(m·N)].Different film structure designs significantly influenced the microstructure，film-substrate adhesion and tribological properties of TiN coatings.The film with the best tribological properties was a gradient TiN film structure.

In order to eliminate the cracks produced during the preparation of Fe-Cr-C-based cladding layers by gas metal arc welding and to broaden their application in harsh impact environments，a wear-resistant and crack-free Fe-Cr-C-based cladding layer with high hardness was designed and prepared by optimizing the composition of the Fe-Cr-C-based powder core wire with Nb，Ti，and B elements.The microstructure，microhardness，and wear resistance of the cladding layer were characterized by scanning electron microscopy (SEM)，energy dispersive X-ray spectroscopy (EDS)，Vickers hardness tester，ultra-depth microscope，and wear testing machine.Results showed that the cladding layer consisted of austenite，eutectic structures and Nb(C，B) hard phases.The Nb(C，B) hard phases were dispersed within the microstructure and acted as pinning agents，resulting in a microhardness of the cladding layer of 900 HV0.2 in the range of 0 to 10 000 μm in depth.Moreover，the Nb(C，B) hard phases，acting as wear-resistant particles during the wear process，prevented micro-cutting and plowing actions of the abrasive particles，thus improving the wear resistance by 76.9%compared to the cladding layer without the addition of Nb，Ti and B elements.The primary wear mechanisms of the cladding layer were abrasive wear and adhesive wear.By optimizing the composition of the Fe-Cr-C powder core wire，the hardness and wear resistance of the cladding layer were effectively enhanced，and the prepared cladding layer was free from cracks.

In order to improve the tritium resistance and corrosion resistance of Al2 O3 ceramic coatings，aluminium oxide coatings were prepared on the surface of aluminium alloys by using micro-arc oxidation technology by individually or simultaneously doping α-Al2O3 nanoparticles and graphene oxide in the electrolyte.The surface morphology，elemental distribution，phase composition，coating thickness and hardness，wear resistance and corrosion resistance of the coatings were analyzed.Results showed that the micro-arc oxidation coating prepared by simultaneously adding 4 g/L α-Al2O3 and 1 g/L graphene oxide to the electrolyte exhibited reduced micropore numbers and smaller pore sizes，resulting in a denser coating compared to the coatings prepared without doping or with single doping.The content of α-Al2O3 in the coating was increased，and the thickness of the coating increased from 23.8 μm to 32.0 μm compared to the undoped coating.The hardness increased from 465.1 HV to 805.2 HV，and the lowest average coefficient of friction was 0.578.The coating prepared by simultaneous doping had a self-corrosion potential of－0.554 V and a self-corrosion current density of 2.145×10－8 A/cm2，exhibiting superior corrosion resistance compared to the undoped and single-doped coatings.

pH value is one of the important factors affecting corrosion in marine environment.The effects of pH value on the corrosion behavior of X100 pipeline steel in simulated seawater were investigated using kinetic potential polarization curves，electrochemical impedance spectroscopy testing technology，corrosion weight loss measurement method，and scanning electron microscopy (SEM) morphology analysis method.Results showed that as the pH value of simulated seawater increased from 7.5 to 9.0，the corrosion rate of X100 pipeline steel showed a trend of increasing first and then decreasing.The anodic region of the kinetic potential polarization curve exhibited a stable passivation interval at pH values of 7.5，8.0 and 8.5.However，when the pH value increased from 7.5 to 8.0，the corrosion rate accelerated significantly.When pH＝8.0，the corrosion potential of X100 pipeline steel became more negative，the corrosion current density was highest，the capacitive arc was smallest，and the corrosion rate reached its maximum.Furthermore，the corrosion products on the substrate surface were thicker，and the corrosion was more severe.When pH＝9.0，the dynamic potential polarization curve showed a clear transition from the dissolution region to the passivation region in the anodic region，with a distinct over-passivation zone.However，when the pH value increased from 8.0 to 9.0，the corrosion phenomenon gradually alleviated，and the corrosion rate decreased instead.

In order to investigate the effects of thermal oxidation surface modification on the properties of NiTi alloys，the effect of preparing oxide films on NiTi alloys by thermal oxidation technique at different temperatures (300～700 ℃) in atmospheric environment was investigated.The research primarily focused on analyzing the morphology，composition，phase structure，phase transformation temperatures and mechanical properties of the Ti-O films formed at different thermal oxidation temperatures.The influence of thermal oxidation on the superelasticity and shape memory effect of NiTi alloys was investigated through tensile tests and water bath heating method.The surface morphology，phase structure，phase transformation temperatures and hardness of the thermally oxidized samples after plane stretching and water bath heating were characterized using scanning electron microscopy (SEM)，X-ray diffractometer (XRD)，differential scanning calorimetry (DSC) and hardness testing.Results showed that at lower thermal oxidation temperatures (300～400 ℃)，the oxide layer formed on the NiTi alloy surface was very thin，and no titanium oxide coating was detected.When the thermal oxidation temperature reached 600 ℃，a dense rutile-TiO2 film formed on the surface，but it was prone to cracking and peeling after tensile deformation，exhibiting poor film-substrate adhesion，which was insufficient to meet practical application requirements.Tensile and water bath heating tests showed that when the thermal oxidation temperature exceeded 400 ℃，the reverse phase transformation of the NiTi alloy during unloading could not be completed，leading to a degradation of its superelastic properties.However，after water bath heating，the B19’→B2 martensitic reverse phase transformation was completed，indicating that high-temperature oxidation did not affect the shape memory effect of the NiTi substrate.These results provided important theoretical and experimental references for studying the film-substrate adhesion and coordination properties of thermally oxidized NiTi alloys.

Chemically bonded phosphate ceramic (CBPC) coatings have often been applied to the surface of 304 stainless steel to mitigate localized corrosion in chloride ion environment.In order to investigate the effect of curing agent types on the corrosion resistance of CBPC coatings in marine environment，four different CBPC coatings were prepared using Al2O3，CaO，SiO2 and ZnO as curing agents.The thermal properties，micromorphology，phase composition，wettability and electrochemical corrosion behavior of these coatings were then analyzed.Results showed that the CBPC coating with ZnO as the curing agent exhibited the highest corrosion potential，the lowest corrosion current density，the largest low-frequency impedance value，and the highest corrosion protection efficiency，which reached 96.49%，demonstrating the best corrosion resistance.This was attributed to the highest relative mass fraction of the AlPO4 phase (20.89%) in the CBPC coating with ZnO as the curing agent.The microstructure of the coating was dense，with fewer corrosion paths.Additionally，the wetting angle of a 3.5%(mass fraction)NaCl droplet on the surface of the coating was the highest，measuring 107°，making it more difficult for the droplet to spread and penetrate the coating surface.In summary，the CBPC coating with ZnO as the curing agent improved the corrosion resistance by reducing the penetration of corrosive media and slowing the corrosion rate.

To improve the corrosion resistance of weathering steel in the atmosphere，two types of iron oxyhydroxide coatings，α-FeOOH and γ-FeOOH，were respectively prepared on weathering steel using a combined method of hydrolysis and ultrasonic deposition.Microscopic morphology analysis (SEM) and X-ray diffraction analysis (XRD) were performed on the coatings.Outdoor atmospheric exposure tests were conducted using three types of specimens: shot-peened only，shot-peened with a prefabricated α-FeOOH coating，and shot-peened with a prefabricated γ-FeOOH coating.The maximum test duration was 4.55 a.Corrosion kinetics test，cross-sectional morphology analysis，X-ray diffraction analysis，open-circuit potential (OCP) test and electrochemical impedance spectroscopy (EIS) test were carried out on the retrieved specimens.Results showed that the prefabricated coatings consisted solely of either α-FeOOH or γ-FeOOH.After the outdoor exposure test，corrosion kinetics measurements indicated that the specimen with the prefabricated α-FeOOH coating exhibited the least thickness reduction.Crosssectional morphological analysis revealed that the specimens with prefabricated coatings developed more compact corrosion layers.XRD analysis demonstrated that the corrosion layer on the specimen with the prefabricated α-FeOOH coating contained the highest proportion of α-FeOOH.Electrochemical tests confirmed that the specimen with the prefabricated α-FeOOH coating exhibited the highest OCP and the greatest rust-layer resistance.In summary，the prepared α-FeOOH coating can promote the formation of corrosion products with the same crystal structure，and improve the corrosion resistance of weathering steel.

To address the issues of the last-stage blades of steam turbines being susceptible to pitting，water erosion and even fracture，surface laser solution-aging strengthening treatment was carried out on 17-4PH precipitation-hardened stainless steel using a rectangular laser spot with dimensions of 22.0 mm×4.9 mm and a focal length of 400 mm.The microstructure，hardness and water erosion resistance of the laser solutionaging strengthened layer under different process parameters were examined and analyzed using optical microscopy，scanning electron microscopy(SEM)，X-ray diffractometer (XRD)，microhardness tester and a water erosion test platform.Results showed that increasing the laser power or decreasing the scanning speed improved the hardness of the strengthened layer.In contrast，higher aging temperatures resulted in microstructural coarsening，which reduced the hardness of the strengthened layer.The experimental results indicated that the water erosion resistance of 17-4PH precipitation-hardened stainless steel after laser solution-aging strengthening was nearly 15 times higher than that of the 17-4PH steel substrate.

An in-depth investigation into the stress corrosion behavior of 20 carbon steel in liquid ammonia and its influencing factors is of great significance.In this study，immersion tests and slow strain rate tension (SSRT) experiments were carried out to examine the corrosion and stress corrosion behavior of 20 carbon steel in liquid ammonia，and to evaluate its corrosion rate and stress corrosion susceptibility.Results showed that，in liquid ammonia，when the experimental pressure increased from 1 MPa to 2 MPa and then to 4 MPa，the corrosion rate of 20 carbon steel increased slightly，and its stress corrosion susceptibility increased.The stress corrosion susceptibility index of 20 carbon steel in liquid ammonia remained consistently above 35%，indicating it was in a highly stress corrosion sensitive region.

In order to address the poor applicability of existing embedded sacrificial anodes in existing reinforced concrete structures，a new type of embedded sacrificial anode applicable to existing reinforced concrete structures was developed.Indoor simulation tests were conducted to investigate the changes in steel reinforcement potential，current，and current density，as well as the corrosion product diffusion behavior of the embedded sacrificial anode in simulated concrete pore solution and in concrete components subjected to chloride salt attack.Results showed that in simulated concrete pore solution，the embedded sacrificial anode was able to fully polarize the steel reinforcement within 6 h.During the service period，the steel reinforcement potential consistently remained more negative than－780 mV，without exceeding the hydrogen evolution potential.In concrete components，the embedded sacrificial anode achieved 80%polarization of the steel reinforcement within 6 h.A single anode provided a stable output current of 0.4 mA，with a current density of 12.74 mA/m2.As the distance between the embedded sacrificial anode and the steel reinforcement measurement point increased，the polarization degree of the steel reinforcement decreased，resulting in a reduced protective effect.The maximum protection distance was determined to be 80 cm.The corrosion products of the anode exhibited diffusive behavior and were distributed as fine white particles within the mortar pores，which could reduce the risk of concrete cracking caused by the expansion of corrosion products.

In order to support the development and application of energy-efficient and environmentally friendly nickel-free cold sealing technologies，a systematic study was conducted to investigate various factors affecting the sealing quality of alkaline nickel-free normal temperature sealing processes.These factors included sealing process parameters (such as pH，temperature，time，surfactants and fluoride ions) and process management variables (such as aging temperature，aging time，and aluminum ion impurities).The sealing quality was evaluated using an online rapid dye spot test，and further verified through a phosphochromic acid weight loss test following nitric acid pre-immersion.Results showed that pH and temperature were the most influential parameters affecting the sealing quality.When the pH value fell below 8 or the temperature dropped below 25 ℃，the sealing quality deteriorated rapidly.Special attention should be paid to the introduction of aluminum ions into the oxidation tank during production management，resulting in turbidity of the bath solution and the formation of sealing ash on the sealed surface，among other issues.When the ambient temperature was below 15 ℃，the sealing film aging process was found to be incomplete，resulting in a weight loss of the sealed pores exceeding 60 mg/dm2 after 24 h of aging.The optimal sealing process control parameters were determined as follows: fluoride ion concentration of 0.4～0.6 g/L，pH value of 8.2～8.6，sealing temperature of 32～35 ℃ and sealing time of 1.2～1.3 min/μm.