Microstructure And Properties Of CoCrFeMnNi High-entropy Alloys Formed By Selective Laser Melting

High-entropy alloys(HEAs)are usually composed of five or more elements in equimolar or approximately equimolar ratios.Due to the unique high-entropy effect and slow diffusion effect,HEAs have excellent mechanical properties,high temperature resistance,corrosion resistance,etc.In this paper,CoCrFeMnNi HEAs were formed by selective laser melting(SLM),and the microstructure and mechanical properties of samples formed at different construction angles were analyzed.The effect of Nb addition on microstructure,mechanical properties and corrosion resistance of CoCrFeMnNi HEAs was studied.The conclusions are as follows:(1)The SLM formed CoCrFeMnNi HEAs is only composed of FCC phase.The XOZ surface of the 0°sample has a"fish-scale"molten pool morphology,with a vertical"layer-layer"interface,and a"track-track"overlap in the horizontal direction.The inside of the molten pool is a columnar epitaxial growth perpendicular to the boundary.grains.As the construction Angle increases from 30°to 90°,the overlap disorder of the molten pool is weakened,and the width of the molten pool becomes narrower and gradually becomes a slender molten channel.(2)The construction direction of 0°sample exhibits a strong<001>orientation,while the90°sample exhibits a higher<101>orientation,and the 45°sample has the weakest texture strength.With the increase of the construction angle,the microhardness of the HEAs first increases and then decreases,and the hardness value of the 45°sample is the highest.The 45°sample has the highest tensile strength of more than 680MPa,while the 90°sample has the lowest tensile strength,but the highest elongation is 38%.Due to the tensile load is parallel to the molten pool direction,the strength of the 90°sample is the lowest.(3)CoCrFeMnNi Nb _X HEAs were prepared by SLM.The Nb0.1 sample showed a dispersed granular Laves phase.The Laves phase in the Nb0.1 sample is distributed diffusely,while the microstructure of the Nb0.15 and Nb0.2 samples becomes white network structure.After adding Nb element,the orientation relationship of grains is weakened,and the grain size is refined.The proportion of HAGBs inside the structure increases,and the toughness of the material is enhanced.(4)With the increase of Nb element content,the hardness of the samples gradually increased,and the hardness value of the Nb0.2 sample was the highest,reaching 425HV.The tensile strength of the Nb0.2 sample reaches 1152MPa,but the elongation is the lowest at 5.7%.The tensile strength of the Nb0.1 samples was 880MPa and the elongation was 22%,achieving a balance of high strength and toughness.The tensile fracture of Nb0.1 sample shows plastic fracture,and Nb0.15 and Nb0.2 are brittle fractures.After adding Nb element,the corrosion resistance of the material has been improved,and the Nb0.1 sample has excellent corrosion resistance.(5)After heat treatment at 980°C and 1080°C,the molten pool characteristics of the Nb0.15 sample disappeared,and the Laves phase particles were dispersed in the structure.The higher the temperature,the smaller the particle distribution,but the grains grew at the same time.After heat treatment,the elongation of the sample is significantly improved,but the strength of the material is significantly lower than that of the as-deposited sample.The fracture morphology is characterized by ductile fracture.