A CoCrFeMnNi high-entropy alloy (HEA) showed elongation to failure ∼ 320% at T = 1023 K and a strain rateε = 10 −4 s −1. Strain hardening and texture weakening occurred at lowε, whereas flow softening and texture strengthening were observed at highε(> 3 × 10 −2 s −1) experiments. The strain rate sensitivity (m) decreased from 0.5 to ∼ 0.25 with increasingε. Deformation with m ∼ 0.5 and deformation-enhanced grain growth at lowε indicated superplasticity associated with grain boundary sliding. The grain boundary diffusion coefficient diminished by a factor of ∼ 4 in the HEA. Concurrent nucleation, growth and cavity interlinkage caused premature failure compared with conventional superplastic alloys. IMPACT STATEMENT FCC CoCrFeMnNi HEA shows superplastic-like flow with ∼ 320% elongation at 1023 K and 10 −4 s −1 strain rate originating from grain boundary sliding.

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