Lattice-distortion dependent yield strength in high entropy alloys

High entropy alloys (HEAs) have attracted great attention due to their impressive properties induced by the severe lattice distortion in comparison to the conventional alloys. However, the effect of severe lattice distortion on the mechanical properties in face-centered-cubic (FCC) and body-centered-cubic (BCC) structured HEAs is still not fully understood, which are critically important to the fundamental studies as well as the industrial applications. Herein, an analytical model for predicting the solid-solution strengthening and the yield stress in FCC and BCC HEAs accounting for the lattice distortion is presented. Both the calculated solid-solution strengthening and the yield strength are compared to the experimental results, to verify the rationality of the built theoretical model. The numerical predictions considering the severe lattice-distortion effect agree well with the experimental results for both FCC and BCC HEAs, in terms of the yield strength and the solid-solution strengthening. Based on theoretical model, the constructed contour line of solid-solution strengthening can be used to evaluate the effect of elemental type on yield strength of HEAs, which provides guideline for discovering and screening the advanced HEAs. Furthermore, it has been identified the atomic-radius mismatch and solid-solution strengthening do not increase directly as the number of components increases in HEAs based on the theoretical analysis. In the Al-x-Cr-Co-Fe-Ni-Mn HEA system, the atomic-radius mismatch and shear-modulus mismatch induced by the added Al element govern the solid-solution strengthening, but this situation disappears in the Al-x-Hf-Nb-Ta-Ti-Zr HEA system. It is further confirmed that the effect of the atomic-radius mismatch on the solid-solution strengthening is obviously higher than effect of the shear-modulus mismatch, dominating the yield strength. These results provide an insight into the effect of severe lattice distortion on the yield strength, and demonstrate a theoretical framework for identifying the desired compositions to create the excellent HEAs.