Nanostructuring as a route to achieve ultra-strong high- and medium-entropy alloys with high creep resistance

Reducing grain size of materials down to the nanoscale regime usually leads to tremendous increase in strength yet at the expense of other key mechanical properties, including creep resistance. Here we demonstrate that nanostructuring endows a CrMnFeCoNi high-entropy alloy and a CrCoNi medium-entropy alloy with excellent combination of extraordinarily high hardness of 11–13 GPa, which is three times higher than those of their coarse-grained counterparts, and much enhanced creep resistance compared with conventional nanocrystalline metals. Grain boundary strengthening and stacking fault strengthening are the two major reasons responsible for the elevated hardness. The combined influence of low stacking fault energy and small grain sizes enables the prosperity of stacking faults, which also accounts for the higher strength of the ternary alloy than that of the quinary one. Theoretical analysis together with microstructural characterization suggest that the increasing interfacial chemical complexity suppresses grain boundary mediated processes, leading to much improved creep resistance with a dislocation-dominant creep mechanism in the nanocrystalline alloys. Our findings shed light on a new perspective for achieving simultaneous ultra-high strength and considerable structural robustness in structural materials.