A precipitation-strengthened high-entropy alloy prepared by selective laser melting in-situ alloying and post-heat treatment

Abstract

Achieving a superior strength-ductility combination for face-centered-cubic (FCC) single-phase high-entropy alloys (HEAs) with outstanding ductility is challenging. However, precipitation strengthening provides an effective method to achieve this. In this study, (CoCrFeNi)94Al3Ti3 HEA was prepared by selective laser melting (SLM) and in-situ alloying of a blend of CoCrFeNi pre-alloyed powders and Al, Ti elemental powders. The blended powders show excellent printability and the as-printed sample exhibits good comprehensive tensile properties, of which the yield strength is 744 MPa, ultimate tensile strength is 901 MPa and the uniform elongation is 25.1%. After aging treatment, the tensile strength of the as-printed sample increased significantly. More importantly, the analysis of the strengthening mechanism reveals that the high-density nano-scale L12-(Ni, Co)3(Al, Ti)-type particles with two different morphologies contribute most of the improved strength for the aged sample. In addition to the strengthening effect from the coherent L12 nanoparticles, both grain refinement due to the occurrence of partial recrystallization and remaining dislocations after aging treatment also improved the strength of the aged sample, with the yield strength and ultimate tensile strength determined as 1164 MPa and 1503 MPa, respectively. Moreover, L21 and σ phases were also introduced into the aged sample, but these incoherent brittle phases without causing serious embrittlement due to their low volume fractions; therefore, the aged sample still achieved a tensile ductility of 10.1%.