Mechanical properties and microstructure evolution of a CrCoNi medium entropy alloy subjected to asymmetric cryorolling and subsequent annealing

Abstract

CrCoNi medium entropy alloy sheets were fabricated by asymmetric cryorolling (ACR) with rolling speed ratios of 1.2 (ACR1.2) and 1.6 (ACR1.6), followed by annealing at 873 K, 973 K, and 1073 K for 0.5 h. The mechanical properties were tested by a tensile test, and the microstructures were examined by transmission electron microscopy (TEM), scanning electron microscopy, and X-ray diffraction. Results show that the tensile strength of the ACR1.6-processed sheet reached 1340 MPa. This ternary alloy exhibits high strength and plasticity with a concomitant improvement in fracture toughness after annealing at 873 K, 973 K, and 1073 K. In addition, ACR1.6-processed sheets displayed better mechanical properties than ACR1.2-processed sheets. TEM results show that the grain refinement and the formation of a large fraction of deformation twins contributed to the enhanced mechanical properties of the CrCoNi medium entropy alloy.