High-γ'nickel-based superalloys are widely used in hot-section components of aero-engines because of their excellent high-temper-ature strength,oxidation resistance,and corrosion resistance.However,conventional cast nickel-based superalloys such as IN738LC usually contain relatively high Al and Ti contents,which readily lead to a wide solidification temperature range,severe elemental segregation,and in-creased cracking susceptibility during laser additive manufacturing.Therefore,reducing the precipitation tendency of detrimental phases and crack formation while maintaining high-temperature strengthening capability is key to realizing the application of IN738LC alloy via laser addi-tive manufacturing.In this study,the Al and Ti contents were each controlled at approximately 3.0％,and the W content was designed at four levels:7.41％,8.41％,9.41％,and 10.41％.The effects of W content on γ'phase stability,detrimental phase precipitation,microstructural evolution,and mechanical properties were investigated. Thermodynamic calculation,laser directed energy deposition(L-DED),heat treatment,phase analysis,microstructural characterization,and mechanical property testing were combined.First,JMatPro software was used to calculate the equilibrium phase constitution of the designed IN738LC alloys.The results showed that increasing W content had a relatively limited effect on the mass fraction of the γ'phase at 900 ℃.When W content increased from 7.41％to 10.41％,the mass fraction of the γ'phase at 900 ℃ increased only from 39.14％to 40.77％.This indicated that,compared with typical γ'-forming elements such as Al and Ti,W was not the dominant element directly increasing the γ'phase content;its main role was to dissolve in the γ matrix and produce solid-solution strengthening.In contrast,increasing W content significantly enhanced the formation tendency of topologically close-packed(TCP)phases.With increasing W content,the mass fraction of TCP phases in-creased from 0 to 4.85％,and their equilibrium precipitation temperature increased from 839 ℃ to 1 051 ℃.This indicated that excessive W significantly increased the risk of detrimental TCP phase precipitation during high-temperature service. Optical microscopy(OM)observations showed that the as-deposited samples exhibited good overall forming quality,with only a small number of pores in local regions and no obvious macrocracks.This indicated that the optimized IN738LC alloy had relatively low cracking sus-ceptibility under the selected L-DED process conditions.After solution treatment and two-stage aging,microstructural uniformity improved,and the γ'phase was uniformly and dispersively precipitated in the matrix.However,relatively obvious second-phase precipitation features remained in the interdendritic regions of the high-W samples.Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)analyses further showed that W content had a significant effect on elemental segregation and carbide formation.In the as-deposited state,Al and Ti were mainly related to γ'phase formation and were relatively stably distributed in the dendrite cores or intragranular regions.With in-creasing W content,the enrichment of W,C,and part of Nb in the interdendritic regions became more pronounced,promoting the formation and coarsening of MC-type carbides.When W contents were 7.41％and 8.41％,the samples showed relatively uniform microstructures with fe-wer detrimental phase precipitates.When W content increased to 9.41％and 10.41％,carbide precipitation became more obvious,and a small amount of needle-like TCP phases were observed after heat treatment.This indicated that excessive W promoted carbide coarsening and TCP phase precipitation,thereby reducing microstructural stability. Mechanical property testing showed that increasing W content improved the hardness and tensile strength of the samples.The Rockwell hardness(HRC)of the as-deposited samples increased from 40.18 HRC(7.41％W)to 42.22 HRC(10.41％W).After solution+two-stage aging,the hardness values of the four samples increased to 40.82,41.64,42.88,43.32 HRC,respectively.The increase in hardness was mainly attributed to the solid-solution strengthening of W and the precipitation strengthening of the γ'phase.Tensile testing showed that the 9.41％W sample exhibited the most pronounced strengthening,with tensile strengths of 1 403 MPa at 25 ℃ and 618 MPa at 900 ℃.However,thermodynamic calculations showed that the TCP phase mass fraction at 900 ℃ for this composition had already reached 2.68％,indicating a clearly increased risk of detrimental phase precipitation.When W content was further increased to 10.41％,grain-boundary carbide continuity and TCP phase precipitation became more significant,leading to decreased plasticity.Fracture morphology observations showed that,with in-creasing W content,the fracture mode gradually shifted from ductile fracture dominated by fine dimples to mixed ductile-brittle fracture. W played a dual role in IN738LC alloy fabricated by laser additive manufacturing.An appropriate amount of W improved alloy strength through solid-solution strengthening,whereas excessive W aggravated interdendritic segregation and promoted MC-type carbide coarsening and TCP phase precipitation,thereby reducing microstructural stability and plasticity.Although the 9.41％W sample exhibited the highest strength,its TCP phase precipitation tendency had already increased significantly,which was unfavorable for long-term high-temperature microstructural stability.In contrast,the 7.41％and 8.41％W samples showed a better comprehensive balance among strength,plasticity,cracking resist-ance,and microstructural stability.Therefore,the W content in L-DED-fabricated IN738LC alloy is recommended to be controlled within 7.41％-8.41％,namely approximately 7.4％-8.4％.This composition range maintains the high-temperature stability of the γ'phase while sup-pressing carbide continuity and excessive TCP phase precipitation,providing a reference for the composition design of nickel-based superalloys specifically intended for laser additive manufacturing.
Aluminum sheaths of high-voltage(HV)cables are susceptible to localized damage induced by the combined effects of environmen-tal corrosion and mechanical stress during long-term service,posing a severe threat to the safe and reliable operation of power grids.According-ly,efficient and reliable in-situ repair techniques are urgently needed.To solve the problem that traditional hot brazing often causes thermal damage to insulation layers during in-situ repair of HV cable aluminum sheaths,cold spray solid-state additive manufacturing(CSAM)has be-come an optimal adternative owing to its superior low-temperature solid-state deposition characteristics.Particle impact velocity is the core pa-rameter determining the deposition and repair quality of cold spray.However,the corrugated curved structure commonly adopted in HV cable aluminum sheaths severely disrupts the distribution of the supersonic flow field,significantly affecting the kinetic behavior of particles.In this study,a three-dimensional numerical model was established based on a coupled computational fluid dynamics-discrete phase model(CFD-DPM)method.The shock wave evolution characteristics on both flat and corrugated curved substrates were comparatively investigated.The velocity attenuation of 5-45 μm particles passing through the shock waves under normal incidence was quantitatively characterized,and com-parative deposition experiments using powders with different classified size fractions were conducted.Simulation results revealed that in the near-wall region of the curved substrate,influenced by shock waves,gas velocity gradients increased sharply;particle velocities decreased most markedly when the particle size was below 15 μm.Experimental results demonstrated that by removing fine powders(optimizing the particle size range to 15-45 μm)and synergistically adjusting the carrier gas pressure to 0.65 MPa,the adverse effects of shock waves were effectively mitigated,yielding denser coatings.By revealing the kinetic energy dissipation mechanism of particles during cold spray onto curved substrates,this study confirmed the feasibility of improving the repair quality of corrugated aluminum sheaths through particle size gradient optimization,providing theoretical support for the development of in-situ repair processes for power equipment.
Suspension plasma spraying(SPS)has emerged as a transformative technology for fabricating next-generation thermal barrier coat-ings(TBCs),driven by the growing demands for higher operating temperatures and efficiency in advanced gas turbines and aero-engines.Con-ventional atmospheric plasma spraying(APS)and electron beam physical vapor deposition(EB-PVD)face inherent limitations in achieving an optimal combination of thermal insulation,strain tolerance,and long-term durability,whereas SPS provides a promising alternative.This technique fundamentally departs from powder-based feedstock routes by injecting a liquid suspension of sub-micron or nano-sized ceramic par-ticles directly into the plasma jet.This review provides a comprehensive and systematic analysis of SPS technology,clarifying its underlying mechanisms,key factors governing coating architecture,resultant performance advantages,and future potential,thereby serving as an authori-tative technical reference for both research and engineering communities. The deposition mechanism of SPS involves a complex sequence of events:penetration and primary atomization of the suspension jet,fol-lowed by secondary fragmentation and rapid evaporation of solvent droplets within the plasma plume.This exposes the fine particles to high tem-peratures,leading to melting or partial melting.The ultrafine molten droplets subsequently impact the substrate or previously deposited layers,where they spread,rapidly solidify,and accumulate.Compared with APS,the use of nanoscale feedstock alters the thermal and momentum his-tory of particles in the plasma,facilitating the formation of unique non-lamellar microstructures.These structures are characterized by finely segmented columns,dense networks of vertical cracks,and high inter-columnar porosity,which are critical to superior performance. The final coating microstructure and properties result from the interplay between suspension characteristics and process parameters.Sus-pension formulation is critical:solvent type(e.g.,water vs.ethanol),through its latent heat of vaporization,affects suspension stability,at-omization behavior,and the thermal load on the plasma.Solute particle size and distribution primarily govern columnar grain refinement and mi-crostructural homogeneity.Solid loading must balance flowability against deposition efficiency;typically,lower concentrations favor more porous structures with higher strain tolerance.Key process parameters,including plasma power,jet chemistry,stand-off distance,suspension feed rate,and substrate conditions(temperature and roughness),must be precisely optimized to control particle melting,adhesion,and coating densification.Through precise regulation of these variables,diverse microstructures ranging from dense vertically-cracked architectures to high-ly porous columnar-dominated morphologies can be designed. These customizable microstructures endow coatings with excellent functional properties.Their defining features—fine columns and vertical cracks—act as intrinsic strain-relief mechanisms and effectively mitigate thermal expansion mismatch and growth stresses.This results in dra-matically enhanced strain tolerance and thermal cyclic fatigue life,farexceeding those of standard APS coatings.The inherent micro-porosity al-so improves thermal insulation.Furthermore,the architectural flexibility of SPS allows the engineering of surface layers with higher density and tortuosity,improving resistance to infiltration by corrosive media such as molten CMAS(calcium-magnesium-alumino-silicate)or water vapor.Mechanically,although SPS coatings may exhibit intermediate hardness and bond strength relative to APS and EB-PVD coatings,their unique fracture behavior provides improved resistance to spallation and erosion. In conclusion,SPS successfully integrates the most desirable characteristics of existing mainstream TBC technologies:within a single scal-able process,it achieves the high strain tolerance and columnar structure reminiscent of EB-PVD while retaining the high deposition rate,geo-metric adaptability,and cost-effectiveness of APS,making SPS a unique spraying technology.
Cold spray technology is based on a low-temperature solid-state deposition mechanism and can effectively suppress oxidation and phase transformation,thereby enabling the preparation of coatings with high bonding strength and low porosity.It is particularly suitable for temperature-sensitive material systems such as Al and Cu.Although Al alloys have the advantages of light weight and excellent corrosion resist-ance,their thermal conductivity and wear resistance are relatively low.Depositing Cu coatings on Al substrates enables property complementari-ty between the two materials.However,cold-sprayed Cu coatings usually suffer from severe work hardening,insufficient strength,and weak in-terfacial bonding.Previous studies have shown that subsequent heat treatment can effectively promote recrystallization,reduce porosity,and im-prove interfacial bonding,but the underlying atomic-scale mechanism remains unclear.Molecular dynamics simulations can reveal key proces-ses such as diffusion behavior and dislocation evolution at the atomic scale.At present,atomic-scale studies on the heat-treatment mechanism of cold-sprayed Cu coatings on Al substrates are still limited.Therefore,this study combined experiments and molecular dynamics simulations to systematically investigate the microstructural evolution of cold-sprayed pure Cu coatings on 6061-T6 Al alloy substrates during heat treatment. In the experimental part,a PCS-100 cold spray system was used to deposit pure Cu coatings on 6061-T6 Al alloy substrates using nitrogen as the working gas at 600 ℃ and 4.5 MPa,followed by heat treatment at 400 ℃.X-ray diffraction(XRD)and scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS)were used to characterize the phase composition and microstructural evolution of the coatings.In the molecular dynamics simulation,a model of a Cu particle with a diameter of 140 Å impacting an Al substrate with dimen-sions of 400 Å×400 Å×200 Å at an impact velocity of 540 m/s was constructed using LAMMPS software and the embedded atom method(EAM)potential.The heat-treatment process at 427 ℃ was simulated,and the atomic-scale structure was analyzed using OVITO software.The experimental results showed that the cold-sprayed Cu coating underwent obvious recrystallization after heat treatment at 400 ℃,and the in-termetallic compound CuAl2 was formed,resulting in a significant improvement in interfacial bonding.The molecular dynamics simulation re-sults showed that,after cold spray deposition,the Cu particle contained a relatively low proportion of disordered structures,but the dislocations were highly entangled and dominated by Shockley dislocations,which accounted for approximately 72％of the total dislocation length,showing typical work-hardening characteristics.In the early stage of heat treatment(100 ps),enhanced atomic thermal vibration reduced lattice stabili-ty,leading to a significant increase in disordered structures,a rapid decrease in dislocation density,and a sharp increase in the number of va-cancies.As the heat-treatment time increased to 800 ps and then 1600 ps,the disordered structures gradually transformed into face-centered cubic(FCC)structures.FCC grains continued to grow as recrystallization proceeded,and the disordered structures decreased and became more uniformly distributed.The number of grains generally exhibited a trend of first decreasing and then increasing,indicating that the microstructure transformed from a highly distorted state to a recrystallized structure.Atomic diffusion analysis showed that Cu atoms preferentially diffused into the Al matrix.This behavior was mainly attributed to the higher diffusion coefficient and larger atomic radius of Al(1.43 Å),as well as the smaller atomic radius(1.27 Å)and higher binding energy of Cu.Heat treatment further strengthened the preferential diffusion tendency of Cu into the Al matrix.The dislocation evolution results showed that the total dislocation length decreased rapidly in the initial stage of heat treat-ment and then tended to stabilize.Shockley dislocations remained dominant throughout the process,and their variation trend was consistent with that of the total dislocation length,whereas perfect,stair-rod,and Hirth dislocations remained at low levels.The number of vacancies showed a"rapid increase followed by slow growth"trend,while the dislocation density decreased significantly in the early stage and then tended to sta-bilize.The synergistic evolution of vacancies and dislocations drove the transformation of the Cu coating from a high-energy non-equilibrium state to a thermodynamically stable state. In summary,this study systematically revealed the microstructural evolution and atomic diffusion mechanism of the cold-sprayed Cu/Al system during heat treatment by combining experiments with molecular dynamics simulations.The results showed that heat treatment significant-ly promoted coating recrystallization,increased the proportion of FCC structures,and caused the number of grains to exhibit a dynamic evolu-tion trend of first decreasing and then increasing.The preferential diffusion of Cu atoms into the Al matrix was significantly enhanced,whereas the reverse diffusion of Al atoms was relatively limited.Meanwhile,the dislocation density decreased rapidly in the initial stage and then tended to stabilize,with Shockley dislocations being dominant,while the number of vacancies continued to increase with time.The synergistic evolu-tion of dislocations and vacancies promoted defect reorganization and annihilation through a thermally activated mechanism,thereby effectively improving the structural stability and interfacial bonding performance of the coating.
WC-based cermet coatings are widely used in marine equipment and chemical valve applications owing to their high hardness,ex-cellent wear resistance,and corrosion resistance.Among them,WC-10Co-4Cr(86WC)is a typical commercial wear-resistant coating system,whereas WC-20Cr3C2-7Ni shows potential advantages in corrosive environments.Studies on the friction-wear-corrosion coupling behavior of these two WC-based coatings in marine environments remain limited.Based on this,73WC and 86WC coatings were prepared on 2507 duplex stainless steel substrates by high-velocity air-fuel(HVAF)spraying,and their microstructures,friction and wear properties,and corrosion re-sistance were investigated. The 73WC and 86WC coatings were prepared by HVAF spraying.The microstructure and phase composition were analyzed by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).The hardness,friction and wear proper-ties,and electrochemical corrosion behavior in 3.5％NaCl solution were tested using a microhardness tester,a pin-on-disk tribometer,and a CHI660E electrochemical workstation,respectively. The results showed that the 73WC coating was mainly composed of WC,Ni,Cr7C3,and(W,Cr)2C phases,whereas the 86WC coating was mainly composed of WC,Co,and a small amount of Co6W6C,with a small amount of W2C also present.Both coatings exhibited dense la-mellar structures and good bonding with the substrate.The thicknesses of the 73WC and 86WC coatings were approximately 179 μm and 212 p.m,respectively,and their porosities were only 0.16％and 0.31％,respectively.The average hardness values of the 73WC and 86WC coat-ings reached 1 182 HV0.3 and 1 286 HV0.3,respectively,both of which were approximately six times those of the substrate.The Weibull modu-lus mof the 73WC coating was 16.80,higher than that of the 86WC coating(8.69),indicating a more stable hardness distribution. Friction and wear results showed that the average friction coefficient of the 73WC coating was approximately 0.32,lower than that of the 86WC coating(0.51).However,its wear rate[(4.26±0.09)× 10-5 mm3/(N·m)]was higher than that of the 86WC coating[(2.54±0.06)× 10-5 mm3/(N·m)].During sliding,Cr2O3 and NiO oxide films formed on the 73WC coating surface,reducing interfacial shear stress.How-ever,the Ni binder phase had relatively low load-bearing capacity,which readily led to WC particle pull-out.In contrast,the Co binder phase in the 86WC coating formed a stable supporting structure,giving better wear resistance. Electrochemical tests showed that the 73WC coating exhibited better corrosion resistance in 3.5％NaCl solution.Its corrosion potential was-421 mV,higher than that of the 86WC coating(-913 mV).Its corrosion current density was only 2.87×10-7 A/cm2,approximately one-eighth that of the 86WC coating.This was mainly attributed to the lower porosity of the 73WC coating and the formation of passive films consis-ting of NiO,Cr2O3,andCr(OH)3. In summary,highly dense WC-based cermet coatings were prepared on 2507 duplex stainless steel substrates by HVAF spraying.The 73WC coating had a lower friction coefficient and better corrosion resistance,making it suitable for marine and chemical corrosive environ-ments.In contrast,the 86 WC coating exhibited better wear resistance owing to its higher hardness and stable Co-based supporting network,making it more suitable for high-load wear conditions.This study revealed the nonsynchronous relationship between friction coefficient and wear resistance in WC-based coatings and clarified the synergistic effects of binder phase stability,microstructural densification,and oxide film evo-lution on comprehensive performance.These findings provide a theoretical basis for the engineering application of WC-based coatings in marine and chemical equipment.
In the field of power transmission and transformation,aluminum components exhibit more complex corrosion behavior under current-carrying conditions.Traditional corrosion prediction methods based on experiments and empirical formulas have limited accuracy and low effi-ciency.In this study,a multimodal prediction method integrating Mamba and a temporal convolutional network(TCN)was proposed.Through the deep fusion of numerical time-series data and surface morphology images,the weight loss of aluminum under current-density and time-gra-dient conditions was accurately predicted.Experimental results showed that the proposed method could effectively capture both short-term fluc-tuations and long-term evolution trends in the corrosion process,even under small-sample conditions.Its prediction accuracy was significantly higher than that of traditional empirical models and unimodal deep learning methods,and the proposed method demonstrated good application potential in material corrosion prediction and intelligent monitoring.
Aluminum(Al),titanium(Ti),and their alloys are ideal materials for aerospace applications owing to their excellent properties,but conventional forming methods still suffer from problems such as oxidation and cracking.In addition,as a lightweight material,magnesium alloy requires further investigation regarding its response mechanism to particle impact.As a low-temperature solid-state deposition process,cold spray technology can effectively alleviate the above problems.However,systematic research on the co-deposition of Al and Ti particles un-der low-pressure conditions remains insufficient.Spraying distance and particle size are key parameters affecting the quality of cold spray depo-sition,while experimental optimization is costly.In this study,numerical simulation and experiments were combined to investigate the effects of spraying distance and particle size on the deposition behavior of Al and Ti particles in low-pressure cold spray.The optimal process parameters were determined to provide a basis for preparing composite coatings on light-alloy surfaces by low-pressure cold spray technology. Fluent software was used to simulate the impact velocity and temperature distribution of Al and Ti particles under a compressed-air pres-sure of 0.9 MPa,spraying temperatures of 200-500 ℃,and spraying distances of 10-30 mum.The optimal spraying distance was determined by preliminary screening at 5 mm intervals,followed by refined simulation within the range of 17-25 mm.Meanwhile,ABAQUS software was used to establish a quarter Lagrangian model for the impact of single Al and Ti particles with particle sizes of 10-30 μm on an AZ31 magnesium al-loy substrate.The equivalent plastic strain(PEEQ)during the impact process was analyzed to determine the critical deposition velocity.The results showed that,when the spraying temperature was 500 ℃,the particle velocity first increased and then decreased with increasing spraying distance,reaching its maximum at a spraying distance of 20 mm.The maximum velocity of 20 μm Al particles was 418.33 m/s,while that of 25 μm Ti particles was 366.29 m/s.At these particle sizes,the velocities of Al and Ti particles were closest to their critical deposition veloci-ties,resulting in the best deposition effect.Under low-pressure conditions,Ti particles were difficult to deposit independently and required Al particles as carriers to achieve co-deposition. To verify the reliability of the simulation results,supersonic low-pressure cold spray experiments were conducted under a compressed-air pressure of 0.9 MPa and a spraying temperature of 500 ℃.First,ball-milled mixed powders with an Al-to-Ti mass ratio of 1∶1 were sprayed at spraying distances of 10,20,25,30 mm.Subsequently,five mixed powders with different particle-size combinations were prepared for com-parison.The experimental results showed that,at a spraying distance of 20 mm,the A20-T25 combination,namely Al with a D50 of approximate-ly 20 μm and Ti with a D50 of approximately 25 μm,exhibited the best comprehensive properties.Its deposition efficiency was 29.97％,aver-age hardness was 154.01 HV0.05,porosity was only 0.59％,friction coefficient was approximately 0.59,and mass wear rate was 1.46×10-11 kg/(N·m).The soft Al phase played a filling and bonding role,while the hard Ti phase provided strengthening and support.The experimen-tal results were in good agreement with the simulation predictions. Through numerical simulation and experimental verification,this study explored the optimal process window for preparing Al/Ti composite coatings by low-pressure cold spray.At a spraying distance of 20 mm and a gas temperature of 500 ℃,Al and Ti particles reached their maxi-mum impact velocities of 418.33 m/s and 366.29 m/s,respectively.The optimal deposition particle size was approximately 20 μm for Al and approximately 25 μm for Ti.This study provided a theoretical basis and process reference for preparing high-performance composite coatings on light-alloy surfaces using low-pressure cold spray equipment.
To address the engineering problem that hot-dip galvanized coatings are prone to corrosion and have insufficient protective service life in high-humidity and high-salt corrosive environments such as marine and industrial environments,this study adopted an organic-inorganic composite superhydrophobic protective system as the design direction.Nano-SiO2 with three particle sizes(30,100,500 nm)was hydrophobi-cally modified with hexamethyldisilazane(HMDS).HMDS-SiO2/PDMS superhydrophobie coatings were then controllably fabricated on hot-dip galvanized substrates by a one-step spraying method.The effects of SiO2 particle size on the microstructure,wettability,wear resistance,and corrosion resistance of the coatings,as well as the intrinsic regulation mechanism,were systematically investigated.Transmission electron mi-croscopy(TEM),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),contact angle measurement,and electrochemical testing were used to comprehensively analyze the structure and properties of the modified particles and coatings.The results showed that low-surface-energy methyl groups were successfully grafted onto the SiO2 surface through chemical bonding by HMDS,causing SiO2 of all three particle sizes to transform from hydrophilic to hydrophobic,with no obvious change in particle size after modification.The opti-mal HMDS-SiO2/PDMS mass ratio required to achieve stable superhydrophobicity increased with increasing particle size:1∶2,1∶1,and 2∶1 for 30,100,and 500 nm SiO2,respectively.The water contact angles of the coatings prepared at the optimal ratios were all higher than 150°.Small-sized HMDS-30SiO2 had a large specific surface area and readily constructed a dense micro/nano rough structure,giving the best initial hydrophobicity with a contact angle of 155.1°.However,insufficient PDMS encapsulation led to poor coating compactness and weak in-terfacial adhesion,and the coating lost its superhydrophobicity after only 15 abrasion cycles.In contrast,large-sized HMDS-500SiO2 had a smaller specific surface area and could be fully encapsulated by PDMS,resulting in a continuous and compact coating structure with strong in-terfacial bonding.Its wear resistance was significantly improved,and the contact angle decreased by less than 2％after 30 abrasion cycles.Electrochemical tests showed that the low-frequency impedance modulus of the HMDS-30SiO2/PDMS coating in 3.5％NaCl solution reached 3.69×105 Ω·cm2,which was three orders of magnitude higher than that of pure zinc.The self-corrosion current density was as low as 1.87× 10-8 A/cm2,and its corrosion resistance was significantly better than that of the pure PDMS coating.Saltwater immersion tests showed that the coating maintained its superhydrophobic state for up to 18 h,and its impedance modulus remained higher than the initial value of pure PDMS after 24 h of immersion.The excellent protective performance originated from the synergistic barrier effect between the coating's physical barrier and the air film trapped by the micro/nano structure:the air film dominated short-term efficient protection,while the physical barrier provided long-term fundamental protection.This study clarified the structure-property relationship between SiO2 particle size and the performance of su-perhydrophobic coatings,and established a trade-off law whereby small particle sizes favored high hydrophobicity and large particle sizes fa-vored high stability.The findings provide systematic experimental evidence and theoretical support for particle size selection,formulation de-sign,and engineering application of superhydrophobic protective coatings on hot-dip galvanized components,and were of great significance for improving the durability and practicality of metal-based protective coatings.
Cold spray(CS),as a low-temperature solid-state deposition technique,can avoid oxidation and phase transformation problems associated with conventional thermal spraying processes.However,it still has limitations,such as insufficient deposition density,difficulty in depositing high-strength and high-hardness materials,and dependence on helium.Laser-assisted cold spray(LACS)introduces synchronous laser heating to achieve localized thermal softening of particles and the substrate deposition zone.While maintaining the characteristics of solid-state deposition,LACS reduces the critical deposition velocity and enhances plastic deformability.This effect improves deposition efficiency,interfacial bonding strength,and coating density,and expands the processing window for cold spraying of difficult-to-deposit materials.This review systematically reviewed the working principle and deposition mechanism of LACS,summarized its research progress in pure metals,structural alloys,high-entropy alloys,and metal-matrix composites,and analyzed the governing mechanism of laser heat input on microstruc-tural evolution and property regulation.Finally,future development directions concerning equipment integration,multi-parameter regulation,and mechanism research were prospected.
Coiled tubing nitrogen operation is a practical technology with broad application prospects.However,due to the presence of oxygen in nitrogen,coiled tubing is prone to corrosion failure in downhole high-temperature and high-pressure environments,posing significant well-control risks.In this study,high-temperature and high-pressure weight-loss corrosion tests were conducted,and scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD)were used to investigate the corrosion behavior of CT90 and CT110 coiled tubing in a simulated downhole nitrogen operation environment(nitrogen purity 95％-99％,temperature 80-120 ℃,pressure 50-90 MPa).The results showed that,in the corrosive nitrogen operation environment,the corrosion rates of CT90 and CT110 in both gas-and liquid-phase environments gradually decreased with increasing nitrogen purity.The change in the liquid phase was more significant,and the corrosion rates of CT90 in both gas and liquid phases were higher than those of CT110.With increasing pressure,the corrosion rates of CT90 and CT110 in the liquid-phase environment both increased.In the gas-phase environment,CT110 showed a gentle upward trend,where-as CT90 first increased slightly and then increased sharply.With increasing temperature,the corrosion rates of CT90 and CT110 in both gas-and liquid-phase environments increased significantly,with the increase in the liquid phase much greater than that in the gas phase.Microscop-ic analysis of corrosion products showed that the main corrosion products on liquid-phase specimens of CT90 and CT110 were Fe3O4 and Fe2O3.The corrosion product films formed in the liquid phase were loose and porous,indicating relatively severe corrosion.Under a single downhole operation time of 10 h and a minimum tensile safety factor of 1.5,evaluation based on the residual tensile strength criterion showed that higher nitrogen purity permitted more downhole operation cycles.Under the same conditions,the maximum number of downhole operation cycles of CT110 was approximately 2.4 times that of CT90.This study analyzed the corrosion morphology and corrosion products of coiled tubing under different conditions,and evaluated the safe service life of coiled tubing in combination with service conditions and failure theory,providing technical guidance for the safe operation of coiled tubing in oilfield production.
Thermoplastic ethylene-methacrylic acid copolymer(EMAA)has attracted widespread attention in fields such as self-healing coat-ings,anti-corrosion coatings,and functional composite coatings because of its good film-forming ability,interfacial adhesion,toughness,and thermally triggered self-healing characteristics.As the demand for adaptability to complex service environments increases in marine engineer-ing,aerospace,oil and gas mining,new energy,and other fields,the mechanical properties,wear resistance,corrosion resistance,erosion re-sistance,and characteristic functionalities of bulk EMAA materials under complex service conditions still require further improvement.This re-view focused primarily on recent research progress in EMAA polymer coatings,and systematically reviewed the material properties of EMAA,chemical and physical modification methods,powder manufacturing technologies,coating preparation processes,and the current status of appli-cation research in typical fields.First,EMAA mainly includes two categories:bulk-polymerized acid copolymers and ionomers modified by metal-ion neutralization.Bulk-polymerized acid copolymers retain more free carboxyl groups and therefore exhibit better polarity,interfacial ac-tivity,and substrate adhesion.In contrast,neutralization-modified ionomers form reversible ionic association structures through the partial neu-tralization of carboxyl groups by metal ions,showing outstanding structural recoverability and functional responsiveness.Current chemical modi-fication of EMAA mainly alters the chemical structure of EMAA macromolecules and the types and distribution of functional groups through chemical reactions;however,related studies on chemical modification remain relatively scarce both domestically and internationally.Physical modification remains the main approach for improving the performance and functionality of EMAA coatings.In this review,the roles of micro/nano particles,such as Al2O3,ZrO2,SiO2,TiO2,and CaCO3,in improving mechanical properties,wear resistance,erosion resistance,and barrier capability against media were systematically summarized.It was also pointed out that one-dimensional or two-dimensional reinforcing phases,such as CNTs,graphene,and boron nitride,are more conducive to increasing the tortuosity of medium transport pathways,inhibiting the penetration of water,oxygen,and corrosive media,and enhancing characteristic functionalities.In terms of fiber reinforcement,carbon fi-bers,glass fibers,basalt fibers,aramid fibers,and other fibers can provide skeletal support for the EMAA matrix,thereby suppressing coating cracking and peeling and improving its mechanical properties,wear resistance,and erosion resistance.Composite modification can achieve multi-component and multidimensional structural optimization through the complementary effects among components with different material sys-tems and dimensionalities,thereby realizing synergistic modification and reinforcement.It can compensate for the insufficient balance in overall performance caused by single-filler modification,allowing the comprehensive performance of EMAA coatings to be fully optimized.Second,in terms of powder manufacturing and coating preparation,EMAA powder preparation techniques mainly include ball milling,screw melt extrusion followed by cryogenic pulverization,as well as emerging technologies such as supercritical CO2-assisted processing and spray drying.The ball milling technique involves a simple process and is suitable for small-batch preparation in laboratories.Screw melt extrusion,combined with cry-ogenic cooling,pulverization,and sieving,offers stronger component-mixing capability,better compositional uniformity,and a more favorable particle size distribution.Moreover,it has the capacity for large-scale production and is currently the most widely used technical route.In con-trast,supercritical CO2-assisted processing and spray drying are highly promising emerging technologies,but their scale-up still requires fur-ther investigation.Regarding coating preparation,thermal spraying technologies,such as flame spraying,are suitable for rapid or convenient on-site construction;electrostatic spraying is suitable for continuous industrial processing of different components;and hot-press molding is more applicable to regular substrates and laboratory sample preparation.
Background and objective:Zn-Al-Mg(ZAM)coated steel sheets are prone to black spot and blackening defects due to Mg oxida-tion,which limits their high-end decorative applications.In this study,a copper nitrate-phosphate chemical oxidation process was used to pre-pare a uniform black decorative film on a medium-Al ZAM coated steel sheet,and its microstructure,mechanical properties,corrosion resist-ance,and coloration mechanism were systematically investigated. Methods:The substrate was a Pangang ZAM coated steel sheet(Mg 2.0％,Al 11.2％,Zn balance;coating thickness 5-8 μm).Speci-mens(50 mm×50 mm×3 mum)were ultrasonically cleaned in acetone,degreased in alkaline solution(15-20 s),activated in 10％HCl(3-12 s),and then chemically oxidized at 37 ℃ for 180-360 s in an aqueous solution containing Cu(NO3)2·3H2 O(1.5-3.0 g/L),Zn(H2PO4)2(4.0-7.0 g/L),anhydrous citric acid(1.5-3.0 g/L),sodium dodecylbenzenesulfonate(0.15-0.30 g/L),and H2O2(5-8 mL/L).Surface and cross-sectional morphologies were observed by scanning electron microscopy(SEM),and elemental distribution was ana-lyzed by energy dispersive spectroscopy(EDS).Phase composition and chemical states were characterized by X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS),respectively.Blackness was quantified using a colorimeter based on the LAB system according to|L|+|a|+|b*|,where a lower value indicates a darker color.Film thickness,roughness,and micro-Vickers hardness were measured using a coating thickness gauge,a roughness tester,and a micro-Vickers hardness tester(load 0.1 kgf,dwell 15 s),respectively.Corrosion resistance in 3.5％NaCl solution was evaluated by potentiodynamic polarization(scan rate 1 mV/s,±0.5 V vs open-circuit potential)and electrochemi-cal impedance spectroscopy(EIS,105-10-2 Hz).Neutral salt spray(NSS)tests were conducted per GB/T 10125-2021[5％NaCl,35 ℃,deposition rate 1-2 mL/(h·80 cm2)],and macroscopic morphologies were recorded at 0,24,312,1 440,1 500,1 600 h. Results:(1)Oxidation process:At 4 min oxidation,the film exhibited a uniform black appearance,with a minimum blackness value of 29.07,thickness 2.63 μm,roughness 0.458 μm,and microhardness 189.2 HV0.1,which was 71.5％higher than that of the substrate(110.3 HV0.1).(2)Microstructure and composition:The film was dense and bundle-like,fully covering the substrate,with a tightly bonded film-substrate interface and no delamination.EDS analysis(mass fraction)gave Zn 56.9％,O 28.6％,Al 5.8％,Cu 2.4％,P 1.6％.XRD and XPS confirmed that the film mainly comprised ZnO,Al2O3,and CuO,among which CuO was the key black-coloring component.(3)Colora-tion mechanism:Pure ZnO is white;the black color originated from CuO absorption of visible light,with phosphate playing a synergistic regu-latory role.Insufficient CuO yielded brick-red Cu2O(reddish tint),while excess phosphate precipitated white Zn3(PO4)2(whitish tint).(4)Corrosion resistance:In 3.5％NaCl,after oxidation the corrosion potential shifted positively from-0.381 V to-0.346 V,the corrosion current density decreased from 2.806×10-6 to 2.219×10-6 A/cm2,and the polarization resistance increased from 1.389×107 to 1.682× 1 07Ω·cm2.EIS showed a significantly enlarged capacitive arc radius and enhanced low-frequency impedance modulus,indicating an improved barrier effect.NSS testing showed no red rust within 1 440 h.After 1 500 h,local film dissolution occurred with reddish-brown rust(Fe2O3/FeOOH);after 1 600 h,corrosion further aggravated. Conclusion:A uniform,dense black film with blackness 29.07,thickness 2.63 μm,and hardness 189.2 HV0.1 was successfully prepared on medium-Al ZAM coated steel sheets via the copper nitrate-phosphate chemical oxidation process.The film structure was dominated by ZnO,while CuO and phosphate synergistically regulated black coloration.The film significantly improved corrosion resistance,with no red rust after 1 440 h NSS testing.This study provides an effective technical route for eliminating surface defects on ZAM coated steel sheets and developing high-quality black decorative films.
Materials are inevitably affected by various factors in natural environments and undergo corrosion.Predicting their corrosion behavior and evolution patterns can provide references for material applicability evaluation and the formulation of protection measures.With the develop-ment of algorithm theory,computer technology,and related software and hardware capabilities,prediction models for material corrosion behav-ior have developed rapidly and attracted wide attention.To improve the understanding of different models and promote their application in corro-sion research,this paper briefly introduced the principles of typical corrosion prediction models,including gray prediction models(GM),sup-port vector machine models(SVM),and artificial neural network models(ANN),and reviewed their application progress in the corrosion field.At present,the theories of the above typical corrosion prediction models have become relatively mature.Their applications primarily in-volved optimizing key algorithmic parameters and computational procedures by incorporating optimization algorithms,thereby improving model prediction accuracy,training speed,and generalization ability.This paper also summarized the model principles and application status of ma-chine learning methods such as deep learning,including convolutional neural networks and long short-term memory networks,and ensemble learning,including random forests and gradient boosting trees.Compared with typical prediction models,these models have more complex structures and stronger prediction and generalization abilities,but they also require larger amounts of data and more computational resources.On this basis,the applicable scenarios,methodological advantages,and limitations of various models were summarized.Finally,the future de-velopment directions of model algorithms were discussed.First,the quality of modeling data samples should be improved by deepening the iden-tification of key corrosion data and standardizing data acquisition and governance.Second,for single-model applications,multiple optimization algorithms should be jointly used to overcome model limitations and improve model learning efficiency and prediction accuracy.Third,with the wider adoption of big data concepts and the explosive growth of data,the application advantages of algorithms such as deep learning and ensem-ble learning are becoming increasingly prominent,and theoretical innovation and computing power optimization are important development di-rections.The integration and complementarity of multiple algorithms to continuously improve the comprehensive prediction ability,generaliza-tion ability,and interpretability of models will be the main development trend of corrosion prediction models.
Titanium alloys are widely used in aerospace,medical devices,chemical equipment,and other fields owing to their high specific strength and excellent corrosion resistance.However,their low thermal conductivity,high chemical reactivity,and low elastic modulus lead to extremely severe tool wear during machining.TiAlN-coated cemented carbide tools are commonly used for cutting titanium alloys,and this coat-ing provides oxidation resistance and a thermal barrier effect.In practical machining processes,cutting tools may be subjected to high tempera-tures,resulting in changes in coating microstructure,release of internal stress,and degradation of the coating-substrate interfacial bonding state.However,the coupled effects of quenching pretreatment,which simulates thermal cycling during interrupted cutting or tool regrinding,and cutting conditions,including dry/wet cutting and cutting speed,on the wear behavior of TiAlN-coated tools have not been systematically investigated.This study aimed to systematically investigate the effects of quenching temperature and cutting parameters on the wear performance of TiAlN-coated cemented carbide turning tools,with emphasis on the rake face wear mechanism,coating adhesion,and cutting temperature rise. TiAlN coatings were deposited on WC-Co cemented carbide substrates by multi-arc ion plating.The deposition process included surface cleaning under a vacuum of 5×10-3 Pa,heating to 480 ℃,and Ar glow cleaning for 60 min,followed by the sequential deposition of a TiAlN bot-tom layer for 30 min,an intermediate layer for 25 min,and an outer layer for 20 min using Ti33Al67 targets.The coating thickness was observed to be approximately 0.97 μm using a scanning electron microscope(SEM;Hitachi Regulus 8100).The coating hardness was measured to be 32.5 GPa using a nanoindenter(Keysight G200).The coated tools were quenched at 200,400,600,and 800 ℃ in a muffle furnace,held for 30 min,and then cooled in a water-oil mixture with a volume ratio of 1:10.The hardness values were measured using an HVS-50Z digital Vickers hard-ness tester under a load of 294 N and were 2 057 HV at 200 ℃,2 062 HV at 400 ℃,2 061 HV at 600 ℃,and 1 986 HV at 800 ℃,while that of the unquenched sample was 2048 HV.These results indicated that the hardness changed only slightly except after quenching at 800 ℃. It was shown by grazing incidence X-ray diffraction(GIXRD;Bruker D8)that,with increasing quenching temperature,the diffraction peaks of both the WC substrate and TiAlN coating weakened,and the full width at half maximum increased,indicating grain refinement but in-creased crack susceptibility.Scratch testing using a WS-2005 tester under a load of 150 N and a scratch length of 6 mum showed that the critical load for coating delamination decreased from 47 N at 200℃ to 26 N at 600 ℃,confirming that the coating adhesion gradually decreased. Cutting tests were conducted on a CK6140S CNC lathe using Ti6Al4V titanium alloy bars with dimensions of φ100 mm×300 mm.The cut-ting parameters were a feed rate of 0.12 mm/r,a cutting depth of 1.4 mm,and cutting speeds of 60,90,150 m/min under dry and wet cutting conditions.The quenched tools treated at 200,400,600 ℃ were tested at 90 m/min under dry cutting conditions.The tool quenched at 800 ℃could not be clamped because of thermal deformation of the mounting hole.The cutting temperature rise was monitored using an embedded ther-mocouple.Under dry cutting conditions,the temperature was 313 ℃ at 60 m/min and 400 ℃ at 90 m/min(a 27.8％increase),and reached 466 ℃ before failure at 150 m/min(a 48.9％increase over 60 m/min). After the tests,the wear regions on the rake face were analyzed by scanning electron microscope(SEM)and energy dispersive spectrome-ter(EDS).Regarding the effect of quenching temperature at 90 m/min under dry cutting conditions,the wear areas were 0.561 1 mm2 at 200℃,0.612 7 mm2 at 400 ℃,and 0.595 5 mm2 at 600 ℃.At 600 ℃,an obvious W signal was detected,indicating substrate exposure and crack formation.Regarding the effect of cutting speed under dry cutting conditions using unquenched tools,the wear areas were 0.473 1 mm2 at 60 m/min and 0.676 4 mm2 at 90 m/min,while the tool failed after only 152 m of cutting at 150 m/min.Under wet cutting conditions using the same water-oil mixture with a volume ratio of 1∶10 and a flow rate of approximately 0.125 L/s,the wear areas were significantly reduced to 0.374 7 mm2 at 60 m/min and 0.399 8 mm2 at 90 m/min,corresponding to 79.2％and 59.1％of those under dry cutting conditions,respec-tively.At 150 m/min under wet cutting conditions,the wear area was 0.915 5 mm2,but the cutting length reached 375 m,approximately 2.5 times that under dry cutting conditions.EDS analysis showed that the atomic percentage of oxygen on the surface ranged from 12.72％to 19.30％,and Ti and Al elements caused by workpiece adhesion were also detected. The quenching temperature had a significant effect on the material properties and wear resistance of TiAlN-coated tools.As the quenching temperature increased from 200 ℃ to 600 ℃,the coating adhesion gradually decreased,and substrate exposure and cracks appeared on the rake face at 600 ℃.Cutting speed played a dominant role in the cutting temperature rise,and higher cutting speeds aggravated tool wear,espe-cially under dry cutting conditions.The use of cutting fluid effectively reduced wear.At 60 and 90 m/min,the wear areas were reduced to 79.2％and 59.1％of those under dry cutting conditions,respectively,and the tool life was extended by approximately 2.5 times at 150 m/min.Quench-ing at 800 ℃ caused severe thermal deformation of the tool mounting hole,making cutting tests impossible.These results provide a quantitative basis for optimizing the quenching process and cutting parameter selection of TiAlN-coated cemented carbide tools in titanium alloy machining.
To address the poor wear resistance of 4340 steel components,WC-10Co4Cr coatings were successfully deposited on 4340 steel sub-strates via high-velocity oxy-fuel(HVOF)spraying and cold spray(CS),with process parameters optimized for each.The microstructure,phase composition,porosity,microhardness,bonding strength,sliding wear,and fretting wear of the two coatings were systematically charac-terized using a scanning electron microscope(SEM),an optical microscope(OM),a X-ray diffractometer(XRD),a Vickers microhardness tester,an universal testing machine,a tribometer,and a 3D profilometer.The effects of CS and HVOF processes on coating structure and prop-erties were compared and analyzed.The results showed significant differences in microstructure,mechanical properties,and wear behavior be-tween the two coatings.The porosity of the CS coating was below 0.1％,whereas that of the HVOF coating was approximately 0.3％.Phase analysis indicated that the WC phase remained stable in the CS coating,while the HVOF coating experienced decarburization of WC and the formation of a new W2C phase.The average microhardness of the CS coating reached 1 617.2 HV0.3,about 52.4％higher than that of the HVOF coating(1 061.3 HV0.3).In sliding wear tests,the wear rate of the CS coating was 1.7 ×10-6 μm3/(N·m),only 39.5％of that of the HVOF coating.Its fretting wear rate was 1.28 μm3/(N·m),37.6％higher than that of the HVOF coating.However,the bonding strength of the CS coating(35 MPa)was significantly lower than that of the HVOF coating(73.5 MPa).In conclusion,compared with the traditional HVOF process,WC-10Co4Cr coatings prepared by the CS process exhibited higher hardness,denser microstructure,and superior sliding wear per-formance,demonstrating promising potential for engineering applications.
Wear is one of the main causes of functional failure in mechanical components,and improving the wear resistance of materials can effectively extend their service life.High-entropy alloy coatings have attracted extensive research attention because of their high-entropy effect,sluggish diffusion effect,lattice distortion effect,and"cocktail"effect.Among them,CoCrFeNi-based high-entropy alloys are one of the cur-rent research hotspots.Increasing the Al content promotes the formation of strong covalent bonds between adjacent atoms,thereby producing a significant solid-solution strengthening effect.When the non-metallic element Si dissolves into the solid solution of high-entropy alloys,it cau-ses severe local lattice distortion,which produces a strong solid-solution strengthening effect and improves the hardness of the alloy.Laser clad-ding is an advanced surface coating preparation technique with high application flexibility and can realize the precision repair of complex struc-tural components.In this process,a high-energy laser beam rapidly melts synchronously fed or pre-placed alloy powder,forming an extremely thin molten pool on the substrate surface,followed by rapid cooling and solidification,thereby producing a dense coating metallurgically bonded to the substrate.Although many studies have been conducted on laser-cladded high-entropy alloy coatings,relatively few have focused on the friction and wear properties of laser-cladded AlCoCrFeNiSi high-entropy alloy coatings.In this study,AlCoCrFeNiSi high-entropy alloy powder prepared by vacuum atomization with a particle size of 15-45 μm was used as the cladding powder,and 40CrNiMoA alloy steel was used as the substrate.AlCoCrFeNiSi high-entropy alloy coatings were prepared on the 40CrNiMoA alloy steel substrate by laser cladding equipment using the coaxial powder-feeding method.Argon was used as the shielding gas,with a flow rate of 15 L/min.The powder feeding rate was 6 g/min,the overlap ratio was 40％,and the laser spot diameter was 2.1 mm.These parameters were kept constant,while the laser cladding scanning speeds were adjusted to 5 mm/s and 8 mm/s,and the laser powers were set to 600,800,1 000 W to obtain the optimal forming parameters.The phase compositions of the AlCoCrFeNiSi high-entropy alloy powder and coatings were analyzed using X-ray diffraction.The surface and cross-sectional microhardness of the AlCoCrFeNiSi high-entropy alloy coatings were measured using a Vickers hardness tester.The elastic mod-ulus of the coatings was determined using a nanoindenter by the static loading method.Friction and wear tests of the high-entropy alloy coatings were carried out using a friction and wear tester at different sliding speeds of 0.04,0.06,0.08 m/s.The wear volume after the friction and wear tests was measured using a laser confocal microscope to calculate the wear rate,and the effects of different sliding speeds on the friction and wear properties of the AlCoCrFeNiSi high-entropy alloy coatings were investigated.The main results were as follows:First,the optimal process parameters for laser cladding of the AlCoCrFeNiSi high-entropy alloy coating were a scanning speed of 8 mm/s and a laser power of 600 W.The coating had a dense microstructure with a BCC phase,and dendritic structures appeared on the surface.Second,the microhardness of the Al-CoCrFeNiSi high-entropy alloy coating was(646±28)HV0.2,approximately 3.5 times that of the 40CrNiMoA alloy steel substrate,which was(180±12)HV0.2.The nano-hardness was(14.4±0.8)GPa,and the elastic modulus was(344±20)GPa.Third,the main failure modes of the AlCoCrFeNiSi high-entropy alloy coatings at different sliding speeds were abrasive wear,adhesive wear,and oxidative wear.With increas-ing sliding speed,the coefficient of friction of the coating increased,the wear rate increased,and adhesive wear became more severe.
Magnesium alloys have low density and high specific strength,making them promising lightweight materials.However,their poor wear resistance under sliding friction limits their application in moving components.Laser cladding can produce high-hardness coatings on mag-nesium alloys and improve their tribological performance.In this study,Ti-Al/TiC composite coatings were fabricated on AZ91D magnesium al-loy.Three energy densities,namely 24.24 J/mm2,16.16 J/mm2,and 12.12 J/mm2,were obtained by varying the laser scanning speed.The changes in microstructure,phase composition,hardness,and wear resistance of the coatings were investigated,and the preferred process pa-rameter was identified. The laser power was fixed at 1 100 W,and the scanning speeds were set to 20,30,and 40 mm/s,corresponding to the above energy densi-ties.Phase composition was analyzed by X-ray diffraction(XRD),and the coatings prepared at all three energy densities were found to consist of AlTi,Al3Ti,and TiC.Scanning electron microscopy(SEM)observations showed that,at 24.24 J/mm2,the microstructure consisted of a mixture of petal-like grains and equiaxed grains,and the TiC particles were coarsened.At 16.16 J/mm2,the coating was dominated by petal-like grains,with fine and uniformly distributed TiC particles.At 12.12 J/mm2,granular grains were observed,and TiC agglomeration occurred. In the hardness test,the average hardness of the magnesium alloy substrate was 83.3 HV0.2.The average surface hardness values of the coatings prepared at 24.24 J/mm2,16.16 J/mm2,and 12.12 J/mm2 were 593.6 HV0.2,726.9 HV0.2,and 687.3 HV0.2,respectively,which were 6.13,7.73,and 7.25 times higher than that of the substrate.The cross-sectional hardness values were also much higher than that of the substrate,and the highest cross-sectional hardness was obtained at 16.16 J/mm2. Friction and wear tests were conducted under a load of 20 N,a frequency of 10 Hz,a stroke of 4 mm,and a test duration of 900 s.The measured average friction coefficients were 0.181,0.171,and 0.185,respectively,and the wear rates were 1.09×10-4 mm3/(N·m),0.93×10-4 mm3/(N·m),and 2.27×10-4 mm3/(N·m),respectively.Wear scar morphology showed that the surfaces of the coatings prepared at 24.24 J/mm2 and 12.12 J/mm2 contained more grooves,abrasive particles,and spalling pits,indicating that the wear mechanisms were abrasive wear and adhesive wear.Fatigue cracks were also observed in the coating prepared at 12.12 J/mm2.In contrast,the worn surface of the coating prepared at 16.16 J/mm2 was relatively smooth and flat,with shallow grooves and small adhesive spalling areas.Wear debris analysis showed that the debris from the coat-ing prepared at 16.16 J/mm2 contained Ti,Al,and O,and TiO2 patches were formed,which provided a certain protective effect. Overall,the energy density had a significant effect on coating quality.At an energy density of 16.16J/mm2,the surface hardness reached 726.9 HV0.2,the friction coefficient was as low as 0.171,and the wear rate was only 0.93×10-4mm3/(N·m),indicating that the wear resist-ance was significantly better than those of the other two groups.The wear mechanism under this condition was dominated by mild abrasive wear and adhesive wear.Therefore,16.16 J/mm2 was considered the preferred energy density for laser cladding Ti-Al/TiC coatings on AZ91D mag-nesium alloy,providing a reference for the surface treatment of wear-resistant magnesium alloy components.
Tubular copper components are core components for fluid transportation and heat exchange and are widely used in industrial fields such as energy,metallurgy,and chemical engineering.However,because of their low hardness and poor wear resistance,these components face a high risk of wear failure,which severely limits their service life.Once damaged,they may cause serious problems such as water leakage,which not only requires equipment shutdown and maintenance but may also lead to production safety accidents and resource waste.Enhancing the wear resistance of tubular copper components through surface coating technology is an important approach to prolonging their service life. To enhance the wear resistance of tubular copper components,plasma cladding was used to strengthen the surface of a small copper tube.The microstructure and properties of the cladding layer were systematically investigated using scanning electron microscopy(SEM),X-ray dif-fraction(XRD),an energy dispersive spectrometer(EDS),a microhardness tester,and a friction and wear testing machine.Based on two cri-teria,namely surface morphology and microhardness,the optimal process parameter combination for preparing the nickel-based cladding layer on the copper tube surface was determined through orthogonal experiments:a preheating temperature of 600 ℃,a plasmaarc current of 140 A,and an arc swing speed of 3 000 mm/min.The obtained cladding layer had a relatively smooth and flat surface,and its average hardness reached up to 616.9 HV0.1. However,because of the limited volume of the small copper tube,the surface temperature of the copper substrate increased rapidly,which easily led to inconsistency between the front and rear sections of the cladding layer,although this inconsistency was not obvious in appearance.Specifically,the rear section showed a higher dilution rate and lower performance.Therefore,the cladding layer prepared under the optimal pa-rameter combination obtained from the orthogonal experiment was further optimized.After the innovative segmented variable-current method was adopted,with the current changed from 140 A in the front section to 130 A in the rear section,the temperature rise of the copper surface during the cladding process was reduced.As a result,the uniformity between the front and rear sections of the cladding layer was significantly im-proved.The average dilution rate was approximately 10％,and the average microhardness was approximately 620 HV0.1. Microstructural characterization showed that significant elemental diffusion occurred on both sides of the interface of the cladding layer,in-dicating the formation of good metallurgical bonding.The cladding layer contained a γ-(Cu,Fe,Ni)solid-solution matrix phase,an interden-dritic Ni3Si phase,and a large number of dispersed Cr-rich phases,including Cr23C6 and CrB.These phases played roles in solid-solution strengthening and dispersion strengthening,respectively,resulting in significantly better performance than that of the copper substrate. Wear resistance tests showed that the copper substrate had a high and severely fluctuating friction coefficient because of its low hardness and poor resistance to plastic deformation.Under shear force,large-area detachment easily occurred on the copper substrate surface,and the wear mechanism was adhesive wear.In contrast,the cladding layer exhibited a lower and more stable friction coefficient.The wear weight loss was reduced by 75.2％compared with that of the copper substrate.The worn surface was mainly characterized by ploughing grooves,and the wear mechanism was abrasive wear. In summary,the preparation of nickel-based cladding layers by plasma cladding can significantly improve the surface properties of small copper tubes,providing theoretical and technical guidance for the surface strengthening of large tubular copper components.In the actual clad-ding process of large tubular copper components,the variable-current regulation method can also be adopted.According to practical conditions,the current can be set as a multi-stage gradient to ensure consistency between the front and rear sections of the cladding layer.In addition,for copper substrates with different volumes,a similar cladding effect can be achieved through simple adjustments of process parameters based on the results of this study.
Heat-resistant steels are extensively used in high-temperature service environments in energy,power,and chemical industries.However,long-term exposure to high temperatures and chloride-containing media can easily lead to surface corrosion and performance degrada-tion.Fabricating FeCrNi alloy cladding layers on heat-resistant steel by powder plasma arc cladding is an effective approach to improving sur-face mechanical properties and corrosion resistance.In this study,FeCrNi cladding layers on a 12Cr2Mo1R substrate were investigated to clarify the effects of heat input regulated by scanning speed on microstructure,mechanical properties,and corrosion behavior. FeCrNi alloy cladding layers were prepared at three scanning speeds of 90,110,130 mm/min under constant process parameters,namely a cladding current of 110 A,ashielding gas flow rate of 15 L/min,and an arc length of 15 mm.The powder particle size was 40-90 μm,and the powder was identified as a single face-centered cubic(FCC)phase.With increasing scanning speed,the macroscopic forming behavior fol-lowed the trend of decreased heat input,reduced molten pool size,and thinner and narrower bead geometry.At 90 mm/min,the molten pool had a relatively high heat input and a long liquid residence time,resulting in a wide and thick bead with coarse surface ripples.At 110 mm/min,the bead morphology was the most regular,the fish-scale ripples were continuous and uniform,the thickness distribution was more con-sistent,and the forming stability was the best.At 130 mm/min,insufficient heat input further reduced the bead width and thickness. Interfacial scanning electron microscopy(SEM)observations showed that,at 90 mm/min,the thermal effect was strong and the metallur-gical reaction was sufficient,while local interfacial discontinuities or metallurgical defects were not readily observed.At 110 mm/min,the in-terface was the straightest and most continuous,and the best metallurgical bonding was obtained.At 130 mm/min,interfacial waviness was in-tensified,and signs of locally incomplete metallurgical fusion were observed. In terms of microstructure,the coating was composed of columnar grains extending along the deposition direction,accompanied by some equiaxed grains.As the scanning speed increased from 90 to 130 mm/min,the heat input per unit length decreased,and the cooling rate was significantly increased.As a result,the microstructure was gradually transformed from coarse dendrites into fine and compact cellular/fine co-lumnar structures,and the sizes of grains and dendritic/cellular structures were markedly reduced.Microstructural refinement led to an increase in hardness.The average Vickers hardness of the coating increased from 237 HV at 90 mm/min to 248 HV at 110 mm/min and further to 261 HV at 130 mm/min. To characterize the mechanical differences in the interfacial microregion,nanoindentation tests were performed at 110 mm/min.The re-duced elastic modulus E*at seven test positions ranged from 262.45 to 337.55 GPa,the indentation elastic modulus EIT ranged from 238.83 to 307.17 GPa,and the indentation hardness HIT ranged from 2 110.81 to 5 112.33 MPa.A representative interfacial point showed E*=293.66 GPa,EIT=267.23 GPa,and HIT=3 712.72 MPa,indicating a significant microscale property gradient near the interface. Corrosion behavior was evaluated in 3.5％(mass fraction)NaCl solution by potentiodynamic polarization(PDP)and electrochemical im-pedance spectroscopy(EIS).It was shown by PDP that,with increasing scanning speed,the corrosion current density generally decreased,and the current density in the anodic passivation region decreased and tended to stabilize,indicating an overall improvement in corrosion resist-ance.However,the electrochemical responses of the samples prepared at 90 and 110 mm/min were relatively close,suggesting that the effect of scanning speed on corrosion resistance was not strictly linear. The EIS results provided a clearer distinction.The radius of the Nyquist capacitive arc increased significantly with increasing scanning speed,indicating that the charge transfer process was increasingly suppressed.Equivalent-circuit fitting showed that the total impedance param-eter Rtotal(R2+R3)was 2.109 0×103 Ω·cm2 at 90 mm/min,3.952 0×103 Ω·cm2 at 110 mm/min,and 1.908 1×104 Ω·cm2 at 130 mm/min,demonstrating that the interfacial charge-transfer resistance and film resistance were significantly improved for the sample prepared at 130 mm/min.Combined with microstructural evolution,it was inferred that microstructural refinement and compositional homogenization in-duced by increased scanning speed weakened interdendritic segregation and micro-galvanic effects,which was beneficial for the formation of a more continuous and compact passive film,thereby improving impedance and corrosion resistance.Scanning speed significantly affected the forming quality,interfacial metallurgical bonding state,and microstructural refinement of the FeCrNi cladding layers by regulating heat input,and further influenced their mechanical properties and corrosion resistance.Overall,with increasing scanning speed,the microstructure tended to become refined,and the properties were synergistically improved.However,the evolution of corrosion resistance did not follow a completely linear trend.These results provided a reference for process parameter optimization and property regulation,while also indicating that the evolu-tion mechanisms of microstructure and properties under the coupled effects of multiple factors require further investigation.
With the increasing complexity of oil and gas extraction environments,the service life of oil well tubing steels faces severe challen-ges,and corrosion is one of the main causes of their failure.Existing corrosion-resistant technologies have limitations such as high cost and in-sufficient performance.China is rich in rare earth resources,but their utilization remains low,and the mechanism by which rare earth elements improve corrosion resistance in steels remains unclear.In this study,low-cost rare earth cerium(Ce)was used to develop an economical rare-earth-modified 5Cr oil well tubing steel for Cl-containing CO2 corrosion environments,aiming to address related challenges and promote the ef-ficient utilization of resources and the high-quality development of the steel industry. Ce microalloying was applied to 5Cr oil well tubing steel to investigate the effects of different Ce contents,namely 0,0.008％,0.031％,and 0.064％by mass fraction,on its resistance to Cl-and CO2 corrosion.The microstructure and inclusion characteristics of the steel were char-acterized by optical microscopy(OM),scanning electron microscopy(SEM),and an energy dispersive spectrometer(EDS).The surface arithmetic mean height(Sa)of the corroded specimens was measured by confocal laser scanning microscopy(CLSM).The cross-sectional ele-mental distribution of the rust layer was observed by electron probe microanalysis(EPMA).The phase composition and elemental chemical va-lence states of the corrosion products were analyzed by X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS),respectively.Polarization curves were measured using an electrochemical workstation to investigate the electrochemical corrosion behavior. The results showed that,with increasing Ce content,the microstructure of 5Cr oil well tubing steel was significantly refined,the morpholo-gy and type of inclusions were markedly changed,and the microstructural uniformity was improved.The addition of rare earth Ce significantly enhanced the corrosion resistance of 5Cr oil well tubing steel,and the improvement in corrosion resistance was positively correlated with the in-crease in Ce content. The surface arithmetic mean height(Sa)of corroded 5Cr oil well tubing steel gradually decreased with increasing Ce content,indicating that Ce addition effectively improved the post-corrosion surface smoothness.Meanwhile,Ce promoted the migration and enrichment of Cr into the rust layer.In particular,the specimen with 0.064％Ce formed a dense and stable dual-layer rust structure after corrosion,with an outer layer mainly composed of chromium oxides and an inner layer mainly composed of iron oxides.This structure effectively blocked the penetration of corrosive media such as Cl-into the substrate.The addition of rare earth Ce significantly optimized the phase composition of the corrosion product film.For the Ce-free specimen(0Ce),the corrosion product film was mainly composed of FeCO3 and Cr2O3.After Ce addition,rare earth oxides such as CeO2 appeared in the corrosion product films of the 0.008％Ce,0.031％Ce,and 0.064％Ce specimens,which significantly improved the stability of the corrosion product film and enhanced its protective effect on the steel substrate. Electrochemical tests showed that,with increasing Ce content,the cathodic polarization curve of bare steel shifted to the left.Ce ions ac-ted as cathodic corrosion inhibitors,were adsorbed onto the substrate,and covered the cathodic active sites,thereby suppressing the cathodic reaction.The corrosion current density(Jcorr)of the corroded steel decreased with increasing Ce content,and the anodic polarization curve shifted to the left,indicating that the compactness of the rust layer was improved and that the corrosion resistance was further enhanced.This study clarified the corrosion-resistance modification mechanism of Ce in 5Cr oil well tubing steel and provided a theoretical basis for the devel-opment of economical 5Cr steels resistant to Cl-and CO2 corrosion.
