Microstructure And Properties Of Al_1.8CrCuFeNi₂ High Entropy Alloy By Selective Laser Melting

High-entropy alloys,as a new type of multi-element alloy material,have many excellent properties such as high strength,high hardness,good wear resistance,corrosion resistance and oxidation resistance.High entropy alloy has important application value in the fields of medical treatment,aerospace and industrial fields.Selective Laser Melting?SLM?is a kind of metal parts direct forming technology.Based on the basic idea of rapid prototyping,this technology has broken through the concept of traditional processing method to remove molding,and has broad development prospects.In this paper,the effect of laser power and annealing on the microstructure and mechanical properties of Al_1.8CrCuFeNi₂ high entropy alloy was investigated.The difference of microstructure and mechanical properties between SLM and vacuum casting was also studied.The main research conclusions are as follows:?1?Taking Al_1.8CrCuFeNi₂ high entropy alloy as the research object,the influence of laser power on the microstructure of the formed part was studied.It was found that with the increase of laser power,the density and mechanical properties of Al_1.8CrCuFeNi₂high-entropy alloy formed by SLM both increase first and then decrease.When the laser power is 275 W,the density of the alloy is over 99%.When the laser power is too high or too low,pores and cracks will appear on the alloy surface,which will reduce the density.?2?According to the XRD results,the phase structure of SLM-formed Al_1.8CrCuFeNi₂high entropy alloy was a single body centered cubic?BCC?solid solution.The cross section and the longitudinal section showed different structure morphologies:the cross section presented the morphology of the long strip molten pool which was parallel to each other.The longitudinal section was a semi-elliptic molten pool with regular gaussian distribution,and the internal grains were mainly columnar crystals growing perpendicular to the molten pool boundary.According to the EDS test results,it can be seen that the element distribution on each forming surface of the alloy was uniform,and there was no obvious element segregation.The phase structure of the arc furnace smelting alloy was mainly BCC solid solution,and the structure was an obvious dendrite structure,which consists of dendrites and interdendritic regions,and there is obvious element segregation.?3?Under the optimal laser power,the microhardness of the cross section and longitudinal section of Al_1.8CrCuFeNi₂ high entropy alloy formed by SLM reaches 870 HV and 905 HV,respectively,and the compressive strength was 1069 MPa,but the plasticity was low?3.3%?.Cross-section wear performance is better than longitudinal section.The strength and hardness of the as-cast alloy were 895 MPa and 593 HV,the fracture strain was 5.3%.The wear amount of as cast alloy was higher than that of SLM alloy.Compared with as-cast alloy,SLM formed Al_1.8CrCuFeNi₂ high-entropy alloy has high strength,hardness,wear resistance and poor plasticity,however both of SLM formed alloys and as-cast alloys have compression fracture characteristics.?4?In order to reduce the porosity and crack,the SLM formed HEA with the highest density were annealed at 1000?.After annealing,the boundary of the molten pool disappeared,and the Cu rich face-centered cubic?FCC?phase precipitated on the BCC matrix.The hardness of the alloy decreased but the plasticity increased,and the pores and cracks were improved.The microhardness of the cross section and longitudinal section of the SLM parts was reduced to 609 HV and 623 HV,respectively.The compressive strength of 1162 MPa with compressive strain of 7.16%and the fracture mechanism was also changed from the original brittle fracture to the brittle-ductile mixed fracture,but the wear resistance was reduced.