Effect of deformation-induced precipitation of B2 phase on superplasticity of Al0.5CoCrFeNiCu high-entropy alloy

The deformation-induced precipitation of B2 phase in high-entropy alloy (HEAs) generally inhibits grain growth, thereby enhancing superplasticity performance. In this study, a duplex fine-grained Al_0.5CoCrFeNiCu HEA with a grain size of 2.30 μm was prepared via large-deformation cold rolling followed by annealing treatment. Excellent TRIP (transformation-induced plasticity) effect was observed at 950 °C and 0.0005 s^–1, achieving a maximum elongation of 1280 %. The fine B2 phase initially inhibits grain growth, enhancing superplasticity during the early stages of deformation. However, as deformation continued, the coarsening of the B2 phase gradually inhibited grain boundary sliding in the matrix, resulting in a decline in the strain rate sensitivity index (m value), as well as secondary stress hardening and macroscopic necking of the specimen. This indicates that the B2 phase plays opposite roles at different stages of superplastic deformation.