Hot Deformation Behaviors Of CoCrFeNiAl_0.1RE High-entropy Alloy

Compared with traditional metal materials,high-entropy alloys have excellent mechanical properties,corrosion resistance and high temperature oxidation resistance.Therefore,high-entropy alloys have become a research hotspot in recent years.However,the grain structure of the as-cast high-entropy alloy is relatively coarse,and there are defects such as voids and looseness,so the actual engineering application value is low.Through thermal processing,the grains can be refined to improve the microstructure and mechanical properties of the alloy.Therefore,thermal deformation behavior and mechanism of the high-entropy alloy need to be studied.In this thesis,the high-temperature compression experiment of CoCrFeNiAlo.iRE high-entropy alloy is carried out to study the relationship between processing map and microstructure evolution,so as to determine the optimal thermal processing parameters.High temperature compression experiments show that the peak stress of CoCrFeNiAlo.iRE high-entropy alloy increases with the decrease of deformation temperature and the increase of strain rate.The thermal deformation activation energy of the alloy was calculated by Arrhenius equation with Zener-Hollomon parameter,which was 411.58kJ/mol.The relationship between peak stress and deformation temperature and strain rate can be described by the following constitutive model:The relationship between flow stress and deformation temperature,strain rate and strain in the whole thermal deformation process can be described by the following constitutive model:The optimum thermal processing range of CoCrFeNiAlo.iRE high-entropy alloy is T=1360-1423K,&=0.001-0.006s"1,and efficiency power dissipation in this region is 33%-41%.T=1273-1345K,&=0.014-1s-1,there may be unstable zones,which should be avoided during hot working.During the thermal deformation process of CoCrFeNiAlo.iRE high-entropy alloy,with the increase of deformation temperature and the decrease of strain rate,the dislocation density gradually decreases,the dynamic recrystallization phenomenon becomes more and more obvious,the crystal tends to be anisotropic and the microstructure is more uniform.The thermal compression process of CoCrFeNiAlo.iRE high-entropy alloy is a typical continuous dynamic recrystallization process.Low angle grain boundaries absorb dislocations and the misorientation angle increases gradually,thus forming dynamic recrystallized grains with high angle grain boundaries.