Research On Microstructure And Properties Of In-situ Particles Reinforced AlCoCrFeNiTi_x High-entropy Alloy Coatings Fabricated By Laser Cladding

High-entropy alloy,as a new type of structural material,presents a simple phase composition and an excellent performance.To satisfy variety performance requirements,the performance regulation of high entropy alloy is becoming a research hotspot gradually.It is reported that there are some problems in alloy strengthening by the means of adding particles,such as burning of the particles,compatibility between the basic metal and the particles,etc.The method of in-situ synthesis of reinforced particle phase is used to improve the microhardness,wear resistance and corrosion resistance of the high-entropy alloy coating in this study.The precipitation of in-situ Ti-enriched particle phase is realized by the doping of Ti element in AlCoCrFeNi high-entropy alloy coating fabricated by laser cladding.In this paper,the microstructure,microhardness,wear resistance and corrosion resistance of AlCoCrFeNiTi_x?x=0,0.2,0.4,0.6,0.8,1.0?high-entropy alloy coatings were investigated comprehensively.The details are as follows:The high-entropy alloy coatings are composed of Fe-Cr solid solution phase,AlNi intermetallic phase,and in-situ TiC particle phase.The coatings doped with Ti atoms show equiaxed grains,and there is a spinodal decomposition structure consisting of Fe-Cr disordered solid solution phase and AlNi ordered intermetallic phase in the grains.The doping of Ti atoms refines the grain of the coating by about 50%,and causes the severe lattice distortion of the AlNi phase.The results of phase stability analysis show that the in-situ TiC particle phase is stable below 1200oC,and the coarsening behavior of AlNi precipitates can be observed after heat treatment at 900oC.With the increase of Ti atoms concentration,the volume fractions of in-situ TiC particle phase in the coatings rise gradually.The average microhardness of the coatings increases from 640HV_0.3 to 860 HV_0.3.There are several strengthening mechanisms in the coatings,such as fine-grained strengthening,solid solution strengthening,second-phase strengthening,and dispersion strengthening.The results of wear tests exhibit that the introduction of in-situ particle reinforced phase significantly enhances the wear resistance of the coatings at room temperature?25oC?and high temperature?600oC?.With the increase of Ti concentration,the volume wear rates of the coatings present a downward trend.In addition,the introduction of in-situ particles in the coating is beneficial to improve the softening resistance of the coatings at high temperature,which inhibits the occurrence of adhesive wear behavior.The main wear mechanism of the Ti₀ coating is adhesive wear and abrasive wear at room temperature,while that of the Ti_1.0 coating is abrasive wear.At high temperature,the wear mechanism of the Ti₀ coating is adhesive wear,abrasive wear,and oxidation wear,and the wear mechanism of the Ti_1.0 coating is mainly oxidation wear and abrasive wear.The Ti_1.0 coating shows the best wear resistance at room temperature and high temperature.The results of electrochemical corrosion tests show that the Ti_1.0 coating possesses the minimum self-corrosion current density in both the active and passive states,indicating that the coating has the best corrosion resistance.The doping of Ti atoms is beneficial to reduce the dimensional passive current density of the coatings.The oxides of TiO₂ and Ti₂O₃ formed by Ti element participating in the cathodic reaction improves the stability and reduces the dissolution rate of the passive film.The introduction of in-situ TiC particles leads to the heterogeneous catalytic effect during the anodic polarization process,which changes the corrosion mechanism of the coatings.The corrosion mechanism of the Ti₀ coating is severe intergranular corrosion and slight pitting corrosion,while that of the coating with Ti atoms doped is pitting corrosion.There are 66 figures,11 tables,and 105 references in this paper.