Strong work-hardenable body-centered-cubic high-entropy alloys at cryogenic temperature

Body-centered cubic (BCC) metals and alloys are usually brittle with limited strain hardening capability at cryogenic temperatures due to the restricted dislocation nucleation and mobility. Herein, we report that decrease of the Nb content in the TiZrHfNbTa0.2 high-entropy alloys (HEAs) can facilitate multiple deformation mechanisms, i.e., dislocation planar slip, strain-induced phase transformations and twinning, at the cryogenic temperature of 77 K due to the decreased phase stability. Particularly, the TiZrHfNb0.3Ta0.2 HEA showed pronounced strain hardening capability and exceptionally high uniform elongation of about 25% with no sign of ductile-brittle transition. Our findings are important not only for providing a prominent family of metallic materials for application at the extreme service conditions, but also for understanding the deformation mechanism of HEAs at cryogenic temperatures in general.