Tailoring the Plasticity of Topologically Close-Packed Phases via the Crystals' Fundamental Building Blocks.

Abstract

Brittle topologically close-packed precipitates form in many advanced alloys. Due to their complex structures, little is known about their plasticity. Here, a strategy is presented to understand and tailor the deformability of these complex phases by considering the Nb-Co µ-phase as an archetypal material. The plasticity of the Nb-Co µ-phase is controlled by the Laves phase building block that forms parts of its unit cell. It is found that between the bulk C15-NbCo₂ Laves and Nb-Co µ-phases, the interplanar spacing and local stiffness of the Laves phase building block change, leading to a strong reduction in hardness and stiffness, as well as a transition from synchroshear to crystallographic slip. Furthermore, as the composition changes from Nb₆ Co₇ to Nb₇ Co₆ , the Co atoms in the triple layer are substituted such that the triple layer of the Laves phase building block becomes a slab of pure Nb, resulting in inhomogeneous changes in elasticity and a transition from crystallographic slip to a glide-and-shuffle mechanism. These findings open opportunities to purposefully tailor the plasticity of these topologically close-packed phases in the bulk by manipulating the interplanar spacing and local shear modulus of the fundamental crystal building blocks at the atomic scale.