Engineering strength, ductility, and thermal stability in medium entropy alloys via controlled processing routes

Abstract

This study investigates the processing-structure-property relationships in CoCrNi medium-entropy alloys (MEAs), aiming to achieve a balanced combination of strength, ductility, and thermal stability. The alloy was fabricated using a three-step process involving spark plasma sintering (SPS), cold rolling, and subsequent annealing. A comprehensive optimization of SPS parameters identified 1050 °C as the optimal sintering condition for achieving high density and favorable mechanical properties. After a 50 % reduction in thickness through cold rolling, annealing treatments ranging from 600 °C to 900 °C were applied. Notably, the sample annealed at 700 °C (A700) demonstrated an exceptional combination of ultimate tensile strength (1018 MPa) and elongation (40.1 %). Microstructural analysis revealed a transformation from equiaxed grains with annealing twins in the as-SPSed state to a high-density defect structure in the rolled condition, including deformation twins, stacking faults, and Lomer-Cottrell locks. The excellent mechanical properties of the A700 sample are attributed to its heterogeneous microstructure, comprising both retained deformed regions and recrystallized grains, with nano-twin networks enhancing ductility and thermal stability. This work presents a novel strategy for tailoring MEAs through controlled processing routes, offering valuable insights for the design of high-performance metallic materials. The findings have broad applicability for optimizing the mechanical properties and thermal stability of other alloy systems through similar processing strategies.