Differential superplasticity in a multi-phase multi-principal element alloy by initial annealing

Multi-phase structure alloys have been widely used in superplasticity deformation due to their ability to inhibit grain growth. However, the current study on multi-phase structure alloys has mainly indicated static grain growth than dynamic grain growth. Dynamic grain growth plays an important role in superplastic deformation because it leads to strain hardening, limiting superplastic elongation. In this research, the Al 0.5 CoCrFeMnNi high-entropy alloy (HEA) was annealed at 1473 K for 2 h to form a single-phase FCC microstructure, then subjected to high-pressure torsion (HPT) for grain refinement. This HEA achieved high-strain rate superplasticity with an impressive elongation of 1100% under a temperature of 1073 K at a strain rate of 10 –1 s −1 . Comparing the results of the present study with a previous work published on the same HEA reveals the impact of initial annealing on the superplastic response. It is suggested that the initial B2, formed during the annealing stage before the HPT process, effectually limits the dynamic grain growth, resulting in remarkably enhanced superplasticity. This investigation introduces the new microstructural evolution to uplift superplasticity in multi-phase structures with dynamic grain growth elimination. Graphical abstract