Excellent combination of strength and ductility of CoCrNi medium entropy alloy fabricated by laser aided additive manufacturing

Abstract

In this study, the CoCrNi medium entropy alloy (MEA) was successfully fabricated by laser aided additive manufacturing (LAAM), a directed energy deposition (DED) process. Results indicate that the ultimate tensile strength (UTS), yield strength (YS), and elongation after fracture (δF) are 873.5 MPa, 620.5 MPa, and 44.8 % respectively. Without any post heat treatment, the as-built state CoCrNi MEA exhibits an excellent combination of strength and ductility. The high YS is mainly attributed to the combination effects from lattice friction stress, boundary strengthening, and dislocation strengthening. Deformation twinning is activated during room temperature tensile deformation, inducing the steady work hardening behavior. Hence, fracture is postponed to higher deformation strain due to the synergistic effect of dislocation gliding and deformation twinning. LAAM is expected to be a versatile and efficient method to fabricate CoCrNi MEA and some other high-performance alloys.