High compressive plasticity refractory medium entropy alloy fabricated by laser powder bed fusion using elemental blended powders

High plasticity light weight refractory complex concentrated alloys (RCCAs) are the best alternative to replace nickel base alloy. The advantages of additive manufacturing (AM) in the rapid and direct forming of complex structure RCCA parts are beyond the reach of traditional techniques. In this work, a simple composition of refractory metal elementals was carefully designed. The single-phase BCC Nb-40Ti-20Ta refractory alloy was fabricated by laser powder bed fusion (LPBF) using elemental blended powders, it has excellent compression plasticity (e>80%) and strength at both room and high temperatures. The effects of laser parameters and treatment process on microstructure and mechanical properties of the Nb-40Ti-20Ta alloy were investigated. The experimental results show that the density and hardness of the alloy are approximately positively correlated with the laser energy density. The laser parameters have a significant effect on the microstructure. Too low energy density leads to the formation of some unmelted powders, while too high power density results in the transformation of micro-pore into larger keyhole. The laser short action time and too rapid cooling rate of the molten pool induce the micro-segregation in grains. beta-phase dendrites are formed from inside to outside while the high melting point Ta acts as the center, and Ti is enriched in the inter-dendrite region. The shapes of grains are divided into two types: columnar and cellular substructures. The single phase BCC Nb-40Ti-20Ta alloy has ultra compressive plasticity whether annealed or not. The results show that the novel alloy prepared by LPBF possesses excellent mechanical properties. This work provides an important progress for the preparation high compressive plasticity RHEAs by LPBF using elemental blended powders.