Selective laser melting of AlCoCrFeMnNi high entropy alloy: Effect of heat treatment

Abstract

The dilemma concerning the trade-off between the strength and ductility of alloys has persistently been a significant problem in engineering applications. Conventional techniques such as grain refinement, severe plastic deformation, and precipitation strengthening usually increase strength at the expense of ductility. High entropy alloys with dual-phase structures, on the other hand, generally display excellent strength-ductility synergy. In this study, we attempted to mix pre-alloyed powders of two distinct phases (body-centered cubic - bcc and face-centered cubic - fcc) to fabricate AlCoCrFeMnNi HEAs with a dual-phase structure by selective laser melting. Furthermore, we investigate the impact of varying heat treatment temperatures (900 °C, 1000 °C, and 1100 °C) on its phase composition, microstructure, and mechanical properties. The results show that with an increase in the heat treatment temperature, the volume of the fcc phase increases gradually and the volume of the bcc phase decreases. The columnar structure in the fcc phase transforms into a cellular structure, and a spinodal decomposition is observed with the bcc phase. As the heat treatment temperature increases, the yield strength decreases while the elongation substantially increases, with the samples heat-treated at 1100 °C showing the best comprehensive properties (yield strength ∼700 MPa, tensile strength ∼950 MPa, and ∼15% ductility).