Effect Of Annealing Treatment On Microstructure And Properties Of CrFeCoNiTi_x High-entropy Alloys Prepared By Powder Metallurgy

High-entropy alloys are diversified in mechanism,structure,properties and applications.High entropy alloys have many excellent properties such as high hardness,excellent thermal stability,wear resistance,corrosion resistance,and excellent low and high temperature mechanical properties,which are due to their four major effects.In this paper,Cr,Co,Fe,Ni and Ti elements are mixed according to a certain ratio.CrFeCoNiTi_x?x=0.2,0.4,0.6,0.8,1.0?high-entropy alloy is prepared by powder metallurgy method.The effects of the atomic size,valence electron concentration,electronegativity and mixed entropy of the annealed high entropy alloy on the structure of the alloy are studied in this paper.XRD is used to analyze its phase.SEM and EDS are used to analyze the surface morphology and composition.The hardness of the alloy is tested by micro-vickers hardness tester.The electric polarization curve is measured by chemical workstation.Finally,the corrosion resistance is studied with nitric acid.The results show that the CrFeCoNiTi_x high entropy alloy is mainly FCC phase,BCC phase,R phase,?phase,Laves phase and HCP phase are secondary phases.The microstructure of the as-sintered and annealed CrFeCoNiTi_x-based high-entropy alloys is similar to that of light gray dendrites?DR?and dark gray interdendritic?ID?structures;The distribution of dendrites is mainly Cr and Ti elements,and the dendrites are mainly distribution of Fe,Co,Ni elements;Ti and Cr have the same BCC crystal structure and similar electronegativity at high temperature.The atomic radii and electronegativity of Ni,Co and Fe are similar,so Ti and Cr can be substituted with each other,and Ni,Co and Fe can be substituted with each other;With the increase of the annealing temperature,the atoms with increased activity overcome the difference in atomic size.This reason allows the atoms to move more freely and causes the intermolecular phase to change.;When annealing at 850?,the hardness of Ti_1.0high entropy alloy reaches 848.2 HV is the maximum,due to the increase of Ti element and the increase of annealing temperature.In the CrFeCoNiTi_x series high entropy alloy,it was found that the annealed Ti_0.2high entropy alloy has improved corrosion resistance compared to the sintered state and the annealed Ti_0.4,Ti_0.6,Ti_0.8,and Ti_1.0high-entropy alloys have lower corrosion resistance than the sintered ones in electrodeposition corrosion.Corrosion resistance of CrFeCoNiTi_x-based high-entropy alloy to 20wt%HNO₃solution,Ti_0.2and Ti_0.4alloys have better corrosion resistance in the as-sintered state than in annealed state;After the annealing treatment,the Ti_0.6alloy,the Ti_0.8alloy and the Ti_1.0alloy have improved corrosion resistance as compared with the as-sintered state.