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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A lamellar (L1 2 + B2) AlCoCrFeNi 2.1 eutectic high entropy alloy (EHEA) was severely deformed by a novel hybrid-rolling process. During hybrid-rolling, the deformation was carried out in two stages, namely cryo-rolling followed by warm-rolling at 600 °C. The strain (ε) imparted in each of these steps was identical ~1.2, resulting in a total strain of ε~2.4 (corresponding to 90% reduction in thickness). The novel processing strategy resulted in an extremely heterogeneous microstructure consisting of retained lamellar and transformed nanocrystalline regions. Each of these regions consisted of different phases having different crystal structures and chemical compositions. The novel structure-composition dual heterogeneous microstructure originated from the stored energy of the cryo-rolling which accelerated transformations during subsequent low temperature warm-rolling. The dual heterogeneous microstructure yielded an unprecedented combination of strength (~2000 MPa) and ductility (~8%). The present study for the first time demonstrated that dual structure-composition heterogeneities can be a novel microstructural design strategy for achieving outstanding strength-ductility combination in multiphase high entropy alloys.

The effect of strain path on microstructure, texture and hardness properties of AlCoCrFeNi 2.1 eutectic high entropy alloy containing ordered FCC (L1 2) and ordered BCC (B2) was investigated. The EHEA was cryo-rolled using UCR, MSCR (during which the samples were rotated by 90° around the ND between each pass) and TSCR(45°) (in which the samples were deformed by unidirectional rolling to half of the total strain and then diagonally rolled for rest half of the strain). The UCR processed material showed a rather heterogeneous microstructure. The textures of the L1 2 /FCC and B2 phases in the MSCR processed material agreed with the cross-rolling texture of the corresponding single phase materials, while the texture of the two phases in the TSCR(45°) processed materials appeared rather weak. Upon annealing at 800°C, the UCR processed materials showed a novel heterogeneous microstructure, while the MSCR and TSCR(45°) processed materials revealed microduplex structure. The heterogeneous microstructure was replaced by the usual microduplex structure at higher annealing temperatures. The annealing texture of the L1 2 /FCC phase showed the presence of α-fiber (ND//<011>) components while the B2 phase showed strong ND-fiber (ND//<111>) components. The UCR processed material with novel heterogeneous microstructure showed much greater hardness as compared to the MSCR and TSCR(45°) processed materials. The present results indicate that strain path exerted significant influence in controlling microstructure, texture and hardness properties of EHEA.