Low-Temperature Annealing Triggered Abnormal Strengthening in a Complex Concentration Alloy via Evolutive Short-Range Ordering.

Abstract

Low-temperature annealing is traditionally employed to relieve residual stresses in metallic materials, typically resulting in softening. However, a novel finding in the face-centered-cubic (fcc) CoNiV medium entropy alloy (MEA) is reported, where low-temperature annealing induces significant hardening without sacrificing ductility. Specifically, after annealing at 530 °C, the yield strength increases from 503 to 653 MPa, while maintaining plasticity of ≈60%. The comprehensive analysis reveals that this unexpected strengthening is attributed to the development of multi-scale chemical short-range orderings (SROs) during the annealing process. These SROs, particularly a newly formed L12-type ordered structure (SRO-2), enhance material strength by promoting dislocation slip planarity and reducing dislocation entanglement. This study demonstrates that low-temperature annealing can effectively optimize atomic-scale structures in complex alloys distinct from that in conventional alloys, thereby improving their mechanical properties. These findings extend the conventional understanding of annealing effects and highlight the potential for leveraging SROs to design high-performance materials.