Superplastic-like flow in a fine-grained equiatomic CoCrFeMnNi high-entropy alloy

Abstract

A CoCrFeMnNi high-entropy alloy (HEA) showed elongation to failure ∼320% at T = 1023 K and a strain rate $ \dot \varepsilon = {10^{ - 4}}\, {{\rm s}^{ - 1}} $ . Strain hardening and texture weakening occurred at low $ \dot \varepsilon $ , whereas flow softening and texture strengthening were observed at high $ \dot \varepsilon ( \gt 3 \times {10^{ - 2}}\, {{\rm s}^{ - 1}}) $ experiments. The strain rate sensitivity (m) decreased from 0.5 to ∼0.25 with increasing $ \dot \varepsilon $ . Deformation with m∼0.5 and deformation-enhanced grain growth at low $ \dot \varepsilon $ 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.

Keywords

• High-entropy alloys
• superplasticity
• strain rate sensitivity
• texture
• cavitation