Microstructure And Mechanical Properties Of Ti₃₀Al₂₅Zr₂₅Nb₂₀ High-entropy Alloys

The discovery of high entropy alloys(HEAs)breaks the rule of phase formation that more components,lead to the more intermetallic compounds and unfortunately mechanical properties.More components and higher mixing entropy than traditional alloys can,on the contrary,form simple solid solutions.So they obtain excellent comprehensive properties such as high strength,high toughness,high temperature stability,good wear resistance and excellent anti-irradiation property.In recent years,HEAs have turned into a new research hotspot in the field of materials.It is found that the HEAs have a certain self-repair mechanism and sluggish diffusion effect after irradiation.Therefore,they have a good application prospect in nuclear cladding materials.However,at present,the research on relevant irradiation mainly focuses on the HEAs composed of Ni,Fe,Co,Cr,Mn and Al,and the irradiation test adopts electron and ion irradiation,which lacks the thermal neutron irradiation performance.Thus,Al,Fe,Mo,Nb,Sn,Zr,Ti,Cr elements with relatively low thermal neutron absorption cross-sections were selected in this project.Fifteen kinds of alloys were designed according to the design principle of HEAs.After screening,melting and detection of phase structure,it was foun d that only Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA had single phase BCC structure.In this paper,the creep behavior and high temperature deformation behavio r of Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA were systematically studied.The effects of peak load and loading rate on the creep propert ies of the alloy were discussed by N ano-indentation experiments.Based on the Gleeble-3500 thermal simulator,the influence of different deformation rates and temp eratures on rheological behavior and microstructure of the alloy Ti₃₀Al₂₅Zr₂₅Nb₂₀ in high temperature was shown;And the thermal deformation of the material model of the alloy Ti₃₀Al₂₅Zr₂₅Nb₂₀ is established.The following conclusions can be drawn:(1)Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA has a simple BCC structure and a preferential orientation on(211)crystal plane.The Young's modulus and Nano-hardness of this HEA measured by CSM are 158.175±5.204GPa and 8.866±0.192GPa,respectively.The creep results show that the creep displacement increases with the increase of the peak load and the loading rate,indicatin g that the creep behavior is related to the loading rate and the peak load.The research result show that the sluggish diffusion effect and preferential orientation of HEAs can improve the creep resistance in a certain degree.(2)Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA has a high value of flow stress,so the compressive strength and compressive plasticity are better.With the increase of deformation temperature or the decrease of strain rate,the flow stress decreases.After deformation,the dendrites were compressed and a b anded structure was also formed simultaneously in the central region.And the larger the strain rate,the more obvious the banded structure.The true stress-true strain curve of Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA is characterized by dynamic recrystallization,which occu rs at grain boundaries and dendrites.The activation energy of Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA was Q=307.3948 KJ/mol.And the thermal deformation constitutive equation based on Arrhenius model is:(?)?=0.005-0.034?+0.280?²-1.101?³+2.321?⁴-2.470?⁵+1.057?⁶n=3.773-1.252?-8.269?²+22.461?³-13.965?⁴-7.619?⁵+8.775?⁶Q=231085.060+1.660×10⁶?-1.143×10⁷?²+4.158×10⁷?³-8.549×10⁷?⁴+9.170×10⁷?⁵-3.939×10⁷?⁶ln A=16.309+167.160?-1178.847?²+4405.332?³-9203.394?⁴+9942.950?⁵-4282.706?⁶.The results above can provide a guidance for the formulation of hot working process of Ti₃₀Al₂₅Zr₂₅Nb₂₀ HEA.