What pins edge dislocations in random alloys? Comparing size and elastic heterogeneities

This work compares the impact of size mismatch and elastic heterogeneities on solute pinning of edge dislocations in random body-centered cubic alloys – solid solutions in which different atomic species occupy lattice sites at random. Using atomic-scale modeling of both parametric alloys and more realistic binary systems (W–Ta and W–Nb) across the full composition range, we show that the mismatch of elastic constants between the alloy constituents can have an effect comparable to, or even greater than, the size mismatch. This contrasts with some solid solution strengthening theories, which assume a homogeneous elastic medium. Our results further demonstrate that the combined effects of size and modulus mismatches are well captured by a quadratic form, consistent with historical phenomenological approaches.