Superplastic behavior of ultrafine-grained Al5Cr20Fe35Co35Ni5 high-entropy alloy

This study highlights the high-temperature superplasticity of the Al5Cr20Fe35Co35Ni5 high-entropy alloy (HEA) with ultrafine grains, capable of exhibiting transformation-induced plasticity (TRIP) at room temperature. Superplasticity was observed in the HEA with a grain size of 0.82 +/- 0.43 mu m, achieved through severe plastic deformation followed by post-annealing. Superplastic flow occurred within the temperature range of 873-1173 K, with 973 K identified as the optimal temperature. At this temperature, the ultrafine-grained microstructure remained stable during deformation, facilitated by the presence of a preexisting B2 phase and the dynamic precipitation of additional B2 phases. The alloy achieved the maximum elongation-to-failure of 420-465 % at strain rates between 5 x 10-4 and 10-3 s-1 at 973 K. The dominant deformation mechanism for superplastic flow was identified as grain boundary sliding, controlled by grain boundary diffusion, with additional contributions from Coble creep at low strain rates. The current HEA stands out for its unique ability to exhibit an exceptional TRIP effect at room temperature and superplasticity at high temperatures, both arising from the same ultrafinegrained microstructure.