Strength improvement of CoCrNi medium-entropy alloy through introducing lattice defects in refined grains

Abstract

Through architecting lattice defects in refined grains, superior mechanical performance of CoCrNi medium-entropy alloy can be achieved without adding alloying elements and/or extra particles. Processing routes including a cold rolling with subsequent annealing were applied on the alloy samples prepared by gas atomization and spark plasma sintering (SPS). On top of the refined grains of f.c.c matrix (∼ 2.35 μm), various lattice defects were also introduced after processing, including high number density of dislocations, stacking faults (SFs), Lomer-Cottrell locks (LCs) and nano-twins, which could significantly improve the mechanical properties. In particular, the yield strength, ultimate tensile strength, and fracture strain of the alloy reached 1.36 GPa, 1.50 GPa, and 7.3%, respectively, after rolling with 70% thickness reduction and annealing at 600 °C for 2 h. The significant improvement in strength is mainly attributed to the refined grains, creation of high dislocation density and other lattice defects, resulting from the innovative processing in SPS, severe deformation and the subsequent annealing.