The effect of local stacking fault fluctuations on dislocation glide and the interplay with solid solution strengthening in Al-Mg alloys

Abstract

Concentrated alloys are characterized by a random arrangement of solute atoms of different sizes, which generates spatially fluctuating displacement and stress fields with non-trivial correlations. This chemical disorder also induces local fluctuations in stacking-fault (SF) energies, giving rise to fluctuating SF forces acting on the partial dislocations bounding the SF. In this work, we investigate the characteristics of the SF noise, including spatial correlations and the impact of such SF energy fluctuations on dislocation glide. Specifically, the gliding behavior of screw, edge, and mixed dislocations in a model concentrated Al-Mg random alloy with varying Mg content is analyzed. The interplay between SF energy fluctuations and solid-solution noise is also discussed. We show that SF forces are spatially correlated, in close analogy with long-range elastic stresses, and exhibit a robust negative correlation along the slip direction. We identify the physical origin of these correlations and demonstrate that they significantly contribute to the critical resolved shear stress for dislocations to glide. In contrast, correlations in other directions are weaker but can still be non-negligible, depending on the underlying interatomic interactions.