Size-dependent strengthening in multi-principal element, face-centered cubic alloys

Multi-principal element (MPE) alloys, sometimes also known as high entropy, complex concentration or multicomponent alloys, have attracted significant attention due to their remarkable mechanical properties, especially face-centered cubic (fcc) CrCoNi-based alloys. In this study, the size effect and strain rate dependence of the strength of equiatomic ternary (CrCoNi), quaternary (CrFeCoNi), and quinary MPE (CrMnFeCoNi) alloys were investigated using in situ strain rate jump (SRJ) micropillar compression tests. No obvious correlation is found between size dependence of strength and the number of elements in these alloys, but an inverse relation is observed between size effect exponent and the Peierls' stress. The single arm source strengthening model was successfully applied on the entire range of samples from the fcc pure elements to fcc equiatomic MPE alloys. Moreover, the activation volumes (~10 b3 to ~100 b3) are consistent among the MPE alloys, indicating the main deformation mechanism is similar in these alloys: dislocation-solute and dislocation-dislocation interactions.