The Effect Of Heat Treatment And Magnetic Field On CuCoCrFeNi High Entropy Alloy's Recrystallization

High entropy alloys(HEAs)are referred to new types of alloy system developed in recent years,which have unique properties that traditional alloys do not have.Scientists have made achievements of HEAs,mostly for the as-cast alloys.However,the alloys with deformation and annealing are rarely involved.Deformation of the alloys followed by annealing will cause changes in the microstructures and performance,which have a great significance for the development of HEAs in plastic forming technology.In this thesis,the deformed high entropy alloy CuCoCrFeNi was heat-treated in two ways: conventional annealing or annealing in a high magnetic field at 6T and 12 T respectively.The effects of heat treatment and magnetic field on the variation of phase structure,grain growth and recrystallization were analyzed,with Vicker's hardness were tested.The results showed that the as-cast high entropy alloys is mainly composed of simple FCC solid solution.Different annealing treatments after deformation did not change the phase structure.After 30%,50% deformation of CuCoCrFeNi alloy and annealed 30 min without magnetic field,so it is clear that primary dendrite grains grow,second dendrite arms gradually disappeared and equiaxed grains appear in the local region;After 70% deformation of CuCoCrFe Ni alloy and annealed 30 min the new grains appear inside the grain of the large distortion degree;internal microstructure of alloy is refined which the annealing time was prolonged to 60 minutes.After 30% deformation of CuCoCrFeNi alloy and annealed 30 min with magnetic field,because of the “pinning effect” of Cu,there are strip grains appearing.The more strip grains appear with the annealing time is prolonged.By means of EDS,it is analyzed that after the ordinary annealing and the annealing under high magnetic field,large amounts of element Cu segregate in the grain-boundary of alloy,which can reach about 60at%;besides,the amount of element Ni is about 20at% which is a little bit more than that of Co?Cr?Fe.By analysis,the effects of magnetic field intensity on the recrystallization of alloy CuCoCrFeNi is weaker than that of the driving force of grain-boundary on the recrystallization.And in the process of annealing,the change of the high-entropy alloy CuCoCrFeN's structure is mainly influenced by the grain-boundary energy.In addition,with the growth of grains,the hardness of high-entropy alloy CuCoNiFeCr also changes.After the holding time of 30 min,this alloy's average grain size is the largest,the structure becomes coarsening and the hardness turns the lowest.Moreover,during the annealing within the magnetic field,the magnet plays a role in the diffusion of elements,and it also decreases the segregation of Cu in the grain boundary of alloy,meanwhile,the hardness of the alloy enhances.