Enhancing Strength-Ductility Synergy of CoCrNi-Based Medium-Entropy Alloy Through Coherent L12 Nanoprecipitates and Grain Boundary Precipitates

Abstract

The L12-strengthened Co34Cr32Ni27Al4Ti3 medium-entropy alloy (MEA) with precipitations of grain boundaries has been developed through selective laser melting (SLM) followed by cold rolling and annealing, exhibiting excellent strength-ductility synergy. The as-printed alloy exhibits low yield strength (YS) of ~ 384 MPa, ultimate tensile strength (UTS) of ~ 453 MPa, and uniform elongation (UE) of 1.5% due to the existence of the SLM-induced defects. After cold rolling and annealing, the YS, UTS, and UE are significantly increased to ~ 739 MPa, ~ 1230 MPa, and ~ 47%, respectively. This enhancement primarily originates from the refined grain structure induced by cold rolling and annealing. The presence of coherent spherical γ' precipitates (L12 phases) and Al/Ti-rich precipitates at the grain boundaries, coupled with increased lattice defects such as dislocations, stacking faults, and ultrafine deformation twins, further contribute to the property’s improvement. Our study highlights the potential of SLM in producing high-strength and ductile MEA with coherent L12 nanoprecipitates, which can be further optimized through subsequent rolling and annealing processes. These findings offer valuable insights for the development of high-performance alloys for future engineering applications.