Solidification,Microstructural And Mechanical Behavior Of A CoCrFeNiCu₄ Non-Equiatomic High Entropy Alloy

Due to its high strength/hardness,good oxidation resistance/creep resistance/corrosion resistance/wear resistance and high temperature softening resistance,high entropy alloys have been widely concerned by researchers at home and abroad,and become one of the key research directions of new materials.In recent years,the concept of alloy design based on high entropy alloy has been broadened from equiatomic alloy to non-equiatomic alloy,It provides a preliminary understanding of the behavior changes of the alloy during various thermal cycles and thermomechanical processes and based on experiments.In this paper,the non-equiatomic CoCrFeNiCu₄ high entropy alloy was prepared by vacuum arc melting.The solidification behavior,recovery recrystallization behavior,microstructure and mechanical properties of the non equiatomic CoCrFeNiCu₄high entropy alloy were systematically studied by X-ray diffraction（XRD）,in-situ X-ray diffraction（in-situ XRD）,differential scanning calorimetry（DSC）,scanning electron microscopy（SEM）and room/low temperature mechanical properties testing.（1）The microstructure of CoCrFeNiCu₄ alloy in as cast,processed and heat treatment States consists of Cu rich phase and CoCrFeNi rich phase,and the melting point is 1140℃and 1175℃respectively.During the heating process,Cu rich particles are superior to those of CoCrFeNi rich particles,and the low melting point Cu rich phase and high melting point rich CoCrFeNi phase show continuous melting and discontinuous solidification.（2）The recrystallization temperature of as cast CoCrFeNiCu₄ alloy is higher than800℃after cold rolling to 90%thinning.Cold rolled alloy:after annealing at 300℃and 500℃,yield strength increase and elongation decrease,the reason may be related to the precipitation of Cu rich particles and elastic rebound;The main reason is the decrease of dislocation density;The yield phenomenon is observed on the tensile curves after annealing at 900℃and 1000℃,and its mechanism needs to be further clarified,but it may be due to the pinning of dislocations by some"gas masses".（3）The yield strength and elongation of CoCrFeNiCu₄ alloy annealed at 700℃,for 1 hour were increased simultaneously in liquid nitrogen environment;In dry ice environment,yield strength increases and elongation decreases.The phenomenon is related to the comprehensive action of dislocation motion ability and deformation twin ability.Under dry ice temperature,the dislocation movement ability is restrained and plays a leading role;Although the dislocation movement ability is restrained to a greater extent at liquid nitrogen temperature,the tendency of deformation twin is greatly improved.