Study On Selective Laser Melting Forming Of FeCoNiAlTi High-entropy Alloy

As a new generation of materials,high entropy alloys(HEAs)have great application potential in machinery and electronics,aerospace,surface coating,etc.with good properties of strength,hardness,corrosion and fatigue resistance.Selective laser melting(SLM)technology breaks through traditional processing technology and has broad application prospects.It has the characteristics of short manufacturing cycle,one-time forming,and no shape limitation.This paper takes FeCoNiAlTi(HEA)as the research object,determines the composition by comparing and analyzing as-cast alloys,prepares pre-alloyed powder by gas atomization,and explores the influence of laser process parameters and annealing treatment on the quality,structure and mechanical properties of the alloy.The main conclusions are as follows:(1)The influence of FeCoNiAlTi(at%)HEA on the mechanical properties of the as-cast microstructure was studied.Fe₂₅Co₂₅Ni₂₅Al₁₀Ti₁₅ HEA and(Fe Co Ni)₈₆-Al₇Ti₇ HEA were designd and prepared.Fe₂₅Co₂₅Ni₂₅Al₁₀Ti₁₅ HEA has BCC+FCC dual-phase structure,presents a typical as-cast dendritic morphology and is accompanied by a variety of nano-particle precipitation.It has high compressive strength and vickers hardness but poor tensile plasticity,which is brittle fracture;while the as-cast structure of(Fe Co Ni)₈₆-Al₇Ti₇ HEA is composed of FCC phase and L1₂ nanoparticles,the compressive strength and vickers hardness are slightly lower than the dual-phase alloy,but the tensile ductility is better.(2)The influence of SLM forming process parameters on the structure and performance is studied.Choose(Fe Co Ni)₈₆-Al₇Ti₇ HEA as the raw material for SLM forming.When the scanning distance is 30?m and the powder layer thickness is 80?m,the shape of the melt channel increases with the increase of the laser power,and first increases and then decreases with the increase of the scanning speed.When P=180W,600mm/s<V<800mm/s,the surface quality of the formed part is the best and the density is up to 99.62%.The alloy has a microscopic dendritic morphology,and the phase composition is FCC solid solution.In terms of performance,the tensile strength and plasticity are significantly improved than the as-cast state,and the elongation reaches 23%.(3)The changes of microstructure and mechanical properties of SLM samples after heat treatment were investigated.The alloy block after heat treatment has good thermal stability,and the crystal structure is still FCC phase.The microstructure is composed of FCC matrix and L1₂nanoparticles.Due to the effect of fine-grain strengthening,the compressive strength and vickers hardness after annealing are increased,while the tensile strength is basically the same as before annealing.