The Microstructures And Properties After Cold Deformation And Annealing Of CrMnFeCoNi High-Entropy Alloy

High-entropy alloy is a new kind of alloy which has only a history of more than ten years,but it has superior properties that traditional materials can not reach.It attracts researchers to participate in this research and has achieved a lot of scientific research results.The sluggish diffusion and lattice distortion effects of high-entropy alloys make its plastic deformation and subsequent recovery and recrystallization properties different from that of traditional alloys.Few studies have been reported in this field so far.In this paper,the effects of cold deformation and annealing on the structure and properties of high entropy alloys are investigated.The research object of this paper is CrMnFeCoNi high-entropy alloy with simple face-centered cubic(fcc)lattice.CrMnFeCoNi high-entropy alloy with nearly equal atomic ratio was prepared by vacuum electric melting furnace refining,casting,electroslag remelting,hot forging and hot rolling.The effect of annealing on the microstructures and properties of CrMnFeCoNi high entropy alloy was studied by metallographic microscope,SEM and TEM,Vickers hardness tester and electrochemical workstation etc.The grain size of CrMnFeCoNi high-entropy alloy hardly changes after cold deformation.The grain orientation of samples with large deformation(cold tensile deformation of 33%)and cold compression(cold compression deformation of 28%)only slightly changes.However,the grain size changes from the original near-equiaxed grain to the directional fine grain with large deformation(cold compression deformation of 28%).The grain orientation tends to {111} [110].It can be inferred that the cold deformation of CrMnFeCoNi high entropy alloy is the result of the synthetical action of intragranular dislocation slip and intergranular slip.The internal grains of cold-deformed alloys annealed at 600 ℃ did not grow almostly,but most of them grew after annealing at 700 ℃ and 800 ℃,especially after annealing at 800 ℃,all the grains size increased greatly,from the original 4.5 μm to about 9 μm.The SEM images of the alloy after electrochemical corrosion show that the electrochemical corrosion morphology of the alloy after cold deformation and annealing is spot corrosion.TEM image analysis shows that dislocation and other defects appear in the grain of the cold-deformed alloy.After annealing,the dislocation density decreases and annealing twins appeared,but no second phase occurred,it indicated that CrMnFeCoNi high-entropy alloy has high thermal stability.In terms of properties,the hardness of CrMnFeCoNi high-entropy alloy increasesd with the increase of cold deformation.The average hardness at the center of the CrMnFeCoNi HEA sample with 56% cold compression is 356 HV.The hardness decreases to about 184 HV after annealing at 800 ℃,in accordance with the hardness before cold deformation.It is concluded that annealing at 800 ℃ was considered as complete recrystallization annealing.It can be inferred that the actual recrystallization annealing temperature of the CrMnFeCoNi high entropy alloy is between 700 and 800 ℃.The corrosion resistance of the alloy decreases with the increase of cold deformation,which is caused by dislocation,vacancy and other defects,it increased the storage energy of deformation in the grain and the high energy state of the system.After annealing,the deformation storage energy of the alloy with the same cold deformation was released and the corrosion resistance was enhanced.The wear resistance of CrMnFeCoNi high entropy alloy specimens after cold deformation is not positively correlated with hardness,which indicated that the wear resistance is the result of strength,hardness,plasticity and toughness.