Dynamic compression responses of heterogeneous-structured CrMnFeCoNi high-entropy alloy at cryogenic temperatures

Dynamic compression experiments are conducted on a heterogeneous-structured CrMnFeCoNi high-entropy alloy (HEA) at different strain rates (1000–5000 s−1) and temperatures (123–293 K) with a split Hopkinson pressure bar system. Yield strength and strain hardening rate increase considerably with decreasing temperature at 5000 s−1 (low-temperature strengthening), but are insensitive to strain rate at 173 K, which can be well described by the Zerilli–Armstrong model. Compared to typical aluminum alloys and homogeneous-structured CrMnFeCoNi HEA, the heterogeneous-structured HEA exhibits higher thermal sensitivity and strain hardening rate. Microstructural characterizations show that dislocation density in the fine-grained domains increases more drastically than in the coarse-grained domains, inducing high deformation gradient between the coarse- and fine-grained domains. At 123 K, nano-scale primary and secondary deformation twins form in grain interior, along with a great number of stacking faults on twin boundaries; the twin width and spacing in coarse grains are considerably higher than in fine grains. In addition, the twin density at 123 K is significantly higher than that at 293 K. Overall, the increased deformation twinning and deformation gradient contribute to pronounced strengthening and strain hardening with decreasing temperatures in the heterogeneous-structured HEA under dynamic compression.