Study On Microstructure And Mechanical Properties Of Ti-Zr-Nb-V-Al High Entropy Alloy

The high entropy alloy with five or more elements as main elements breaks the traditional alloy design concept and has the characteristics of high entropy effect,delayed diffusion,serious lattice distortion and "cocktail" effect.At present,most of the refractory high entropy alloys are expensive and have high density,which is not conducive to industrial application.In addition,most existing high entropy alloys do not have tensile plasticity,so it is urgent to solve the defects of high density,poor plasticity existing in high entropy alloys.In order to develop new high temperature structural materials,high entropy Ti-Zr-Nb-V-Al alloys with refractory metal elements as main components was prepared by vacuum arc melting.The effects of Al,Ti,Zr content and heat treatment process on microstructure and mechanical properties of the alloy were studied.Alloy(Ti2Zr)xNbVAly can be divided into three series:first,x=0.5,y=0.5,0.75,1.0,1.25(TZ0.5 series for short);second,x=1.0,y=0.5,0.75,1.0,1.25(TZ 1.0 series for short);third,x=1.5,y=0.5,0.75,1.0,1.25,1.75,2.0(TZ 1.5 series for short).Thermo-cal software and TCNI-8 database phase diagram are used to calculate and predict the phase composition of(Ti2Zr)xNbVAly series high entropy alloy,which is verified by experiments.The results show that only when x=1.5,y=0.5 or 0.75,the phase diagram calculation results are consistent with the experimental results and are all composed of a single BCC solid solution phase.Other alloys consist of unordered BCC and ordered BCC phases,except when the alloy withx=0.5 and y=1.25 contains a small amount of intermetallic compound.The morphology of the microstructure is dendrite,the interdendritic is enriched with Al and Zr elements,and is poor in Nb elements,and the distribution of Ti and V is relatively uniform.The addition of Al can significantly improve the strength and hardness of the alloy and reduce the plasticity of the alloy,wherein the yield strength of the(Ti2Zr)0.5NbVAl1.0 alloy is 1365 MPa,but the plasticity is less than 30%,while the yield strength of the(Ti2Zr)1.5NbVAl0.5 alloy is 914 MPa but has a good plastic deformation of>60%.On the basis of the above work,the alloy(Ti2Zr)1.5NbVAl0.5 with the best compressive plasticity was selected,and the effects of holding time and heat treatment temperature on the micro structure and tensile mechanical properties of the alloy were systematically studied.Annealing treatment was carried out on the alloy with 50%cold rolling deformation.The results show that the alloy after heat treatment still maintains single-phase BCC with equiaxed crystal structure,with the minimum grain size of 34 μm and the maximum grain size of 389 μm.The increase of heat treatment time and temperature decreases the yield strength and tensile strength of the alloy and increases the plasticity of the alloy.When the heat treatment conditions are 900℃ and 30 min,the tensile plasticity of the alloy is the best,which is 8.44%.