Microstructure And Properties Of Laser Remelted Layer On Al_xCoCrFeNi High Entropy Alloy

The Al_xCoCrFeNi high entropy alloy has been extensively studied and possesses good mechanical performance,corrosion resistance,wear resistance,and thermal stability.Its manufacturing methods primarily include smelting casting and powder sintering.As-casted Al_xCoCrFeNi high entropy alloy with coarse grains,and more pores in the sintered alloy,thus reducing their wear resistance.In order to improve the surface wear resistance of Al_xCoCrFeNi high-entropy alloy,the Al_xCoCrFeNi high-entropy alloy substrate was prepared by vacuum arc melting and discharge plasma sintering respectively,and then the surface was remelted by laser technology.The microstructure,mechanical properties,friction and wear properties of the laser remelted layer were analyzed and examined.The main findings are as follows:The comparative results reveal that the remelted Al_0.7Co CrFeNi high entropy alloys with cast laser surface can significantly reduce the grain size.The near surface area of the remelted layer is a fine isoaxial crystal,while the near fusion area is a columnar crystal,and its direction is perpendicular to the substrate.Sintered laser surface remelted Al_0.7Co CrFeNi high entropy alloys can reduce,even eliminate pores in the matrix and improve material compactness.Laser surface remelted Al_0.7Co CrFeNi high entropy alloy plays a role in fine crystal strengthening,and the hardness of the remelted layer largely increases.The hardness of the as-casting state is higher than that of the sintered matrix,and the hardness of the remelted layer is slightly higher than that of the sintered state.Laser surface remelted Al_0.7Co CrFeNi high entropy alloy can significantly reduce the coefficient of friction and wear rate,improve surface wear resistance.As Al content increases,the remelted layer on the Al_xCoCrFeNi high-entropy alloys evolved from FCC to FCC+BCC and then to BCC structures.The grain sizes of the surface layers of laser remelting Al_0.3Co CrFeNi,Al_0.7Co CrFeNi and Al_1.0Co CrFeNi alloys are approximately 6?m,5?m and 4?m,respectively.As Al content increases,the grain size of the remelted layer on the surface of the Al_xCoCrFeNi alloy decreases.The relative amount of BCC in the surface layer is higher than that of its matrix,indicating that laser remelting is conducive to forming BCC phase.With the increase of Al content,the hardness of the surface layer on the Al_xCoCrFeNi high-entropy alloy increases,and its friction coefficient and wear rate reduce,and the surface wear resistance improves.From the precipitation evolution and wear resistance of nitrides in the remelted surface layer on the Al_xCoCrFeNi high entropy alloy.Laser remelting is protected by nitrogen,and the Al N phase generats distributing at the grain boundary,with the increase of Al content,the relative amount of Al N phase increases,and the distribution density increases accordingly.The heat capacity and thermal conductivity of nitrogen are larger,the cooling rate of the molten pool under nitrogen protection is faster,and the solidification rate of Al_xCoCrFeNi high-entropy alloy increases,promoting the formation of BCC phase in the remelted layer.Therefore,when Nitrogen compared to argon protection,the relative amount of BCC phase in the surface layer of Al_xCoCrFeNi high entropy alloy is remelted by laser.Coupled with the formation of the Al N phase,the surface hardness is greater,so the coefficient of friction and wear rate are lower,and the surface wear resistance is better.