New advances in metastability engineering for strengthening and toughening high-entropy materials

Unique combinations of different strengthening mechanisms can be invoked in the multicomponent high-entropy materials (HEMs) to achieve excellent mechanical properties within their practically infinite compositional space. For instance, apart from the intrinsic massive solid solution strengthening effect, a joint activation of twinning- and transformation-induced plasticity effects can be realized in a series of high-entropy alloys (HEAs) by rendering them metastable. In this talk, we will introduce some of our recent ideas associated with the metastability engineering for strengthening and toughening multicomponent HEMs. The first is about triggering “high-stress twinning” in ultrastrong HEAs of very high stacking fault energy (~80 mJ/m²), which in turn promote the good ductility. The second refers to an unexpected sluggish martensitic transformation in a strong and super-ductile HEA of ultralow stacking fault energy (~7 mJ/m²), where chemical short-range orders and lattice distortions play roles in the deformation. The third represents the concept of strengthening and toughening high-entropy ceramics (HECs) by incorporating with dispersed metastable ceramic phases. The associated mechanisms behind these ideas will be clarified and discussed.