Ab initioexamination of ductility features of fcc metals

Abstract

Through systematic density-functional theory-based ab initio calculations, various performance indicators such as $G/B$, the ratio of shear modulus $G$ over bulk modulus $B$, ${\ensuremath{\sigma}}_{s}/{\ensuremath{\sigma}}_{t}$, the ratio of ideal shear strength ${\ensuremath{\sigma}}_{s}$ over tensile strength ${\ensuremath{\sigma}}_{t}$, and the Cauchy pressure defined as ${C}_{12}\text{\ensuremath{-}}{C}_{44}$ were evaluated for a selection of fcc metals and assessed in relation to the characteristics of their electronic distributions obtained from the electron localization function. The analysis reveals that the ratio ${\ensuremath{\sigma}}_{s}/{\ensuremath{\sigma}}_{t}$ is possibly a better indicator of malleability as it discriminates directionally bonded metals in addition to discerning ductile crystals from brittle ones. Furthermore, Al is found to sustain the largest shear deformation among the scrutinized solids due to its directional bonds. Similarly, the surprisingly long range of distortion of Pd is rationalized as a result of the geometric constraints caused by small electron pockets of comparatively high localization in the interionic region. However, the examination of the peculiar case of Ir suggests that, in general, the extent of shear distortion should be the consequence of at least two factors, namely, the angular characteristics of bonding and the bond strength.