Achieving ambient superformability in a lightweight refractory medium-entropy alloy via stagewise adaptive microstructural buffers

Lightweight refractory high- and medium-entropy alloys (LRH/MEAs) are being explored as potential materials for lightweight applications owing to their low densities, high strengths, and excellent strength-to-weight ratios. However, their limited ductility and formability under ambient conditions restrict their broad industrial applications, particularly in the manufacturing of highly valuable, hot-sectional parts with complex geometries. Although recent studies have advanced the understanding of ductilization in these alloys, practical solutions to overcome the ambient ductility and formability limitations remain elusive. Here, we report an exceptional superformability in ambient cold-rolling of a strong-yet-ductile Ti₅₀V_29.5Zr₁₀Nb₁₀Mo_0.5 (at. %) LRMEA, achieving a remarkable elongation of 1600 % at a thickness reduction of 96 %, without the need for intermediate stress-relieving annealing. The observed superformability arises from the adaptive buffering microstructures that evolve during the cold-rolling process, namely, slip and kink bands in the early stage, kink and shear bands in the moderate stage, and shear bands and dislocation channels in the late stage. These localized microstructures act as adaptive stress buffers, effectively mitigating stress concentrations, and thereby preventing crack initiation and propagation. After cold-rolling annealing at 400 °C for 1 h, the 0.2 mm-thin LRMEA strip reaches an ultrahigh yield strength of 1.5 GPa while maintaining a sufficient elongation of 10 %. These findings demonstrate that the engineering of stagewise adaptive microstructural buffers is a promising strategy for mitigating stress concentrations and achieving superior performances. This strategy can be utilized in the future design of ductile, superformable refractory alloys, such as LRH/MEAs, with potential applications in engineering sectors that require high-strength, lightweight thin strips.