Effect Of Annealing Treatment On Microstructure Evolution And Properties Of CoCrFeNiTi_xB_y High Entropy Alloy Prepared By Powder Metallurgy

As a superalloy that subverts traditional design concepts,high-entropy alloys have broad prospects in industrial applications due to their excellent performance.Therefore,since the very moment when high-entropy alloys were born,they have attracted huge attention and extensive research from a large number of scientific researchers,and have become a research hotspot in the field of materials.Although high-entropy alloys have developed rapidly and achieved groundbreaking results in just a dozen years,and even related research has been strongly supported by government agencies in various countries,the research on high-entropy alloys is still in its infancy.The alloying mechanism,deformation mechanism,diffusion mechanism and strengthening mechanism of the alloy,as well as the basic scientific issues involved in it,are insufficiently understood.In the current study,different Ti and B elements are added on the basis of CoCrFeNi high entropy alloy.The effect of Ti element content on CoCrFeNiTi_xB_0.05（x=0.2,0.4,0.6,0.8,1.0）high-entropy alloy and B element content on the microstructure and mechanical properties of CoCrFeNiTi_0.6B_x（x=0.025,0.05,0.075,0.1,0.125,0.15）high-entropy alloy was systematically studied,and the effect of heat treatment at different temperatures on its structure and properties was also studied.The experiment selects Co,Cr,Fe,Ni,Ti metal powder and B powder with a purity of not less than 99%.The raw materials are prepared by powder metallurgy.After annealing treatment at 450℃,650℃,and 850℃respectively,OM and XRD are used.SEM,EDS,Vickers hardness tester and other means to characterize,test and analyze the microstructure and mechanical properties.The study found that the CoCrFeNiTi_xB_y high-entropy alloy is mainly composed of FCC phase with a small amount of BCC phase and borides;the microstructure of the sintered and annealed CoCrFeNiTi_xB_y high-entropy alloy is similar,consisting of dark gray interdendrites and light gray dendrites microstructure composition;as the annealing temperature increases,atoms are activated,continue to diffuse,change the intermolecular phase,and the hardness gradually increases;with the increase of Ti content,the interdendritic Ti-rich phases increase,and the BCC structure phases increase,which increases the hardness of the alloy;With the increase of B content,hard boride appears in the alloy,which is beneficial to increase the hardness of the alloy.In the sintered state,CoCrFeNiTi_0.6B_x（x=0.15）reached the maximum hardness of 251.67HV,and CoCrFeNi B_0.05Ti_x（x=1.0）reached the maximum hardness of302.32HV;when annealing at 850℃,CoCrFeNiTi_0.6B_x（x=0.15）reaches the maximum hardness of 508.94 HV,and CoCrFeNi B_0.05Ti _x（x=1.0）reaches the maximum hardness of 533.32 HV.