The Taming of the Screw: Dislocation Cores in BCC Metals and Alloys

Abstract: Body-centred cubic (BCC) transition metals tend to be brittle at low temperatures, posing significant challenges in processing and major concerns for damage tolerance. The brittleness is largely dictated by the screw dislocation core; the nature and control of which remain a puzzle after nearly a century. Here, we introduce a physics-based material index {chi}, the energy difference between BCC and face-centred-cubic structures, that guides manipulation of core properties. The lattice friction and nucleation barrier have near-linear scaling with {chi} and the core transforms from non-degenerate to degenerate when {chi} drops below a threshold in BCC alloys. {chi} is related to solute valence electron concentrations and can be quantitatively predicted by first-principles calculations, providing a robust path for design of ductile and tough BCC alloys.