Towards stronger high-entropy alloy by nanoprecipitation-hardened ultrafine-/nano-grains

Every strengthening/hardening method has its own limit. However, it is difficult to couple multiple extreme hardening in a bulk material, especially for highly strengthened ones. Here we demonstrate a strategy to further harden an ultrastrong precipitation-hardened high entropy alloy (HEA) with ultrafine-grain (UFG)/nanograin (NG) bands. These UFG/NG bands with nanoprecipitates were obtained by combining local severe plastic deformation (SPD) from cryogenic rolling and the pinning effect of precipitates during recrystallization. We found that the bands, with combined hardening of NGs and nanoprecipitates, provide an amazing yield strength of ~2.8 GPa and an ultrahigh hardness of ~9.7 GPa. Such nanoprecipitation-hardened UFG/NG bands in the bulk HEA contribute to an extra strengthening close to 300 MPa and an extremely high tensile strength of more than 2.2 GPa. This research presents a possibility for obtaining NG structure in bulk metals which will open new avenues for developing stronger alloys.