Effect Of C Alloying On Mechanical Properties And Corrosion Behavior Of A CrFeCoNi High-entropy Alloy

Alloying has been widely used to improve the mechanical properties of multicomponent high-entropy alloys.Among them,C plays a significant role in strengthening of high-entropy alloys and has not been systematically studied in the CrFeCoNi high-entropy alloys.Therefore,We designed a series of（CrFeCoNi）-xC（x=0,0.25,0.5,3 at.%）alloys with various carbon additions for systematical research.The alloys were prepared by arc melting and drop cast,followed with homogenization,cold rolling and recrystallization.The influence of carbon alloying on the high-entropy alloy,including phase structure,microstructure,tensile properties and corrosion behavior,was studied.Firstly,the effects of low carbon content（0.25 and 0.5 at.%C）alloying on the phase structure and microstructure of CrFeCoNi high-entropy alloy after solidification and homogenization were studied.The microstructures of the（CrFeCoNi）-0.25C and（CrFeCoNi）-0.5C high-entropy alloys are composed of coarse grains and single phase face-centred cubic（FCC）structures after solidification.Element segregation is observed in the solidification structures,in which Cr is segregated in the interdendrites,whereas Fe,Co and Ni elements are segregated on the dendrite.After homogenization at1200℃/6 h,the elemental segregation has been basically eliminated.Secondly,the effects of low carbon content（0.25 and 0.5 at.%C）alloying on the microstructure and tensile properties of CrFeCoNi high-entropy alloys after recrystallization were studied.The microstructures of the two alloys are composed of equiaxed and annealed twins.The（CrFeCoNi）-0.25C alloy is a single-phase FCC structure.The（CrFeCoNi）-0.5C alloy is composed of equiaxed grains and spherical Cr₂₃C₆ carbides,which are distributed unevenly in grain boundaries and intragrains.With the increase of carbon content,the yield strength and tensile strength of the alloys increase gradually.Finally,the effects of high carbon content（3 at.%C）alloying on the phase structure,microstructure,tensile properties and corrosion behavior of CrFeCoNi high-entropy alloy after recrystallization were studied.The（CrFeCoNi）-3C high-entropy alloy precipitates more spherical Cr₂₃C₆ carbides,which are distributed unevenly in the grain boundary and intragrains.After annealing at 800℃/1 h,the yield strength of the（CrFeCoNi）-3C alloy is 767 MPa,and the tensile strength is 957.7 MPa.However,the precipitation of carbides reduces the corrosion resistance of the alloy,and pitted holes appear on the surface.In this paper,the results show that the alloying of carbon C of CrFeCoNi high-entropy alloys is evidenced to be effective for strengthening,which plays a certain role in the development of CrFeCoNi high-entropy alloys.