Study On Microstructure And Properties Of Ti_xAlCrNbV Refractory High-entropy Alloy

The refractory high-entropy alloy has high melting point and high entropy alloy characteristics,exhibits excellent high-temperature performance,and is expected to become a new generation of high-temperature alloy,which has attracted widespread attention at home and abroad.In this paper,TiAlCrNbV,Ti1.5AlCrNbV and Ti2 Al Cr NbV refractory high entropy alloys were prepared by cold-wall induction skull melting system?ISM?based on the concept of high entropy alloys.The microstructure and mechanical properties of the as-cast and annealed alloys,high-temperature oxidation resistance,and high-temperature thermal deformation of the alloy were studied.The phase composition of TixAlCr NbV alloys were predicted by high entropy criterion and solid solution criterion.The phase composition and microstructure of the as-cast and annealed alloys were analyzed by XRD,SEM and EDS.The alloy mechanics was analyzed by room temperature compression,high temperature compression and hardness test.It was found that the as-cast TixAlCrNbV high entropy alloys consist of a simple body-centered cubic solid solution phase.When x=1 and 1.5,the annealed alloy precipitates the high hardness Laves C14 phase on the body-centered cubic matrix.The alloys have strong hardness and strength.The hardness of as-cast and annealed TiAlCrNbV alloys are 689.5HV and 740 HV,respectively.The as-cast and annealed room temperature strengths of Ti1.5CrCrNbV alloys are 1561 MPa and1660MPa,respectively.The alloys have good high temperature performance.The yield strength of Ti_1.5Al Cr NbV alloy is 1100 Mpa at 750?and 667 Mpa at 850?.Study on the high temperature oxidation behavior and oxide layer structure of high entropy alloys revealed that the oxidation products of TixAlCrNbV high entropy alloys are various,including TiO2,Al2O3,?Ti0.6Al0.2Nb0.2?O2,Ti0.8Cr0.1Nb0.8O2,V2O5,AlVO4.The oxides are distributed in layers.There are a total of three different layers:the first layer is a mixture of TiO2,Ti0.8Cr0.1Nb0.1O2,?Ti0.6Al0.2Nb0.2?O2 and other oxides.The second layer is a mixture of Al2O3,V2O5 and AlVO4.The third layer is the diffusion layer of oxygen.The content of Ti affects the oxidation resistance of TixAlCrNb V high-entropy alloy.Too little elemental content of Ti does not generate enough TiO2 on the surface of the sample to prevent oxygen from entering.Oxygen atoms can easily enter the diffusion layer of oxygen with less TiO2 protection.Too much elemental content of Ti leads to a corresponding decrease in the composition of Al,which leads to a reduction in the amount of Al2O3 formed.Furthermore,the poisoning effect of V on Al2O3 leads to a decrease in the oxidation resistance of the alloy,thus increasing the Ti content in the alloy.The study of the thermal behavior of high entropy alloys revealed that the alloy deformation is divided into three stages:the first stage is the work hardening stage,the second stage is the stress reduction stage,and the third stage is the steady state stage.The increase of deformation temperature and the decrease of deformation rate are beneficial to the dynamic recovery and dynamic recrystallization of two softening mechanisms,reducing the work hardening effect.The thermal activation energy of Ti1.5AlCrNbV high entropy alloy is 319.201 KJ/mol when the deformation temperature is from 1000°C¹200°C and the deformation rate is from 0.1s^-10.001s^-1.The constitutive equation is:???=0)0)^22.53[sinh?0.00664563?]^2.14exp?-319201/?The dynamic recrystallization mechanism of the alloy is discontinuous dynamic recrystallization.When dynamic recrystallization does not occur,the deformed structure exhibits an elongated flow line perpendicular to the deformation direction,and the recrystallized grains nucleate at the grain boundary where the original deformation is large.