Optimal interplay of charge localization, lattice dynamics and slip systems drives structural softening in dilute W alloys with Re additives

Abstract

Body centered cubic metals, such as tungsten (W), and their alloys exhibit superior mechanical properties such as high tensile strength and hardness, but their limited ductility contributes to brittleness and causes challenges in manufacturing and machining. While the ductilizing effect of Re additives in dilute W alloys is well reported, a fundamental understanding of the variations in elastic properties with temperature as well as the optimal composition that drives the softening mechanism, is warranted. Here we employ a combination of ab initio molecular simulations and experimental characterization to probe the structural softening in dilute W-Re alloys. We reveal that the coupled effect of charge localization around Re atoms and the predominance of softer phonon modes for a W alloy with 3.1 at.% Re results in the lowest values for the elastic moduli. We develop a probabilistic theory based on the likelihood of Re atoms to be located on the 〈111〉 family of slip directions, to explain the optimum fraction of Re that enhances the structural softening in the alloy. In essence, we corroborate that softening is realized through a reduction of intervening and mutually obstructing slip systems, interlinked with the electronic structure and lattice dynamics.