Edge dislocations in multi-component solid solution alloys: Beyond traditional elastic depinning

Abstract: High-entropy alloys (HEA) form solid solutions with large chemical disorder and excellent mechanical properties. We investigate the origin of HEA strengthening in face-centered cubic (FCC) single-phase HEAs through molecular dynamics simulations of dislocations, in particular, the equiatomic $\rm CrCoNi$, $\rm CrMnCoNi$, $\rm CrFeCoNi$, $\rm CrMnFeCoNi$, $\rm FeNi$, and also, $\rm Fe_{0.4}Mn_{0.27}Ni_{0.26}Co_{0.05}Cr_{0.02}$, $\rm Fe_{0.7}Ni_{0.11}Cr_{0.19}$. The dislocation correlation length $\xi$, roughness amplitude $R_{a}$, and stacking fault widths $W_{SF}$ are tracked as a function of stress. All alloys are characterized by a well defined depinning stress ($\sigma_c$) and we find a novel regime where exceptional strength is observed, and a fortuitous combination takes place, of small stacking fault widths and large dislocation roughness $R_{a}$. Thus the depinning of two partials seems analogous to unconventional domain wall depinning in disordered magnetic thin films. This novel regime is identified in specific compositions commonly associated with exceptional mechanical properties ($\rm CrCoNi$, $\rm CrMnCoNi$, $\rm CrFeCoNi$, and $\rm CrMnFeCoNi$). Yield stress from analytical solute-strengthening models underestimates largely the results in these cases. A possible strategy for increasing strength in multi-component single-phase alloys is the combined design of stacking fault width and element-based chemical disorder.