Composition Optimization And Performance Study Of CuxCoCrFeNi High Entropy Alloy

High entropy alloys are a new type of alloys that have been rapidly developed in the 21 st century.Their high strength,high hardness,and high wear resistance make them have broad application prospects.In recent years,the design concept based on high entropy alloys has been expanded from isoatomic alloys to non isoatomic alloys.Non isoatomic alloys are receiving increasing attention.This study is based on Cu_xCoCrFeNi high entropy alloys to change the content of Cu elements.Using molecular dynamics simulation method,the effects of Cu content,temperature,and strain rate on the mechanical properties of the system’s high entropy alloy under uniaxial tension were mainly studied.At the same time,the effects of Cu content,temperature,and strain rate on the microscopic evolution,dislocation evolution,and shear strain of the system’s high entropy alloy were also studied from an atomic microscopic perspective;Secondly,using molecular dynamics simulation method,the effect of Cu content on the mechanical properties of the system’s high entropy alloy under nanoindentation was studied,as well as from a microscopic perspective;Finally,Cu_xCoCrFeNi high entropy alloy was prepared by vacuum arc melting,and its microstructure and mechanical properties were tested.The main research results are as follows:（1）The yield stress and Young’s modulus of Cu_xCoCrFeNi high entropy alloys are negatively affected to varying degrees by increasing Cu content and temperature.The increase in Cu content will greatly increase the yield strain of the high entropy alloy in this system,while the increase in temperature will still decrease the yield strain.In contrast,an increase in the strain rate will increase both the yield stress and the yield strain,but the Young’s modulus will decrease.The increase in Cu content increases the FCC structure,while other structures gradually decrease,and the dislocation density is relatively stable.Increasing temperature has little effect on the structure of each phase,but the dislocation density gradually decreases.The increase in the strain rate has little effect on the structure and dislocation density of each phase.Increasing Cu content,temperature,and strain rate will increase the shear strain and gradually distribute evenly.（2）Under the action of nanoindentation,Cu_0.1CoCrFeNi high entropy alloy has the fastest load growth and peak load reaching speed.With the increase of Cu content,the peak load gradually decreases.Increasing Cu content will also gradually decrease the hardness of the high entropy alloy in this system,but the decrease is not significant.After the completion of loading,the crystal structure and phase composition of the high entropy alloy with Cu content of each component remain basically unchanged,with the FCC structure accounting for the majority.The number of dislocations will decrease from a relatively stable number.With the increase of Cu content,the shear band gradually extends beyond the indentation.（3）Cu_xCoCrFeNi high entropy alloy has a simple crystal structure.Increasing Cu content will transform the alloy from a single-phase FCC structure to a two-phase FCC structure,and the position of the main peak does not change with increasing Cu content.When the Cu content is low,the morphology of the high entropy alloy is relatively simple,and the grain boundary is not obvious.Mainly the first FCC structure.Increasing the Cu content can make the morphology become a typical dendritic structure,the second FCC structure is very obvious.When the Cu content is low,the tensile surface of the high entropy alloy undergoes necking,and there are some grooves like morphologies.Increasing the Cu content will cause more grooves like and steps like morphologies to appear on the tensile surface.When the Cu content reaches the maximum,the necked portion contains a large number of slip bands in different directions.Observing the fracture dimples of each component can indicate that each tensile sample has obvious ductile fracture.The yield strength and microhardness of Cu_xCoCrFeNi high entropy alloy are both low,reaching the highest value when the Cu content is 0.1.Increasing the Cu content will cause more and more precipitation of Cu-rich phase,resulting in a slow decline in the yield strength and microhardness of the alloy,but the plasticity will become better and better,indicating that the high entropy alloy has good tensile deformation ability.