Extra-electron induced covalent strengthening and generalization of intrinsic ductile-to-brittle criterion

TLDR

Traditional strengthening mechanisms such as strain, precipitation, and solid‑solution work by pinning dislocation motion, while the brittle, high‑strength behavior of Al₁₂W‑type compounds arises from their fivefold icosahedral cages common to quasicrystals and bulk metallic glasses. The study uses first‑principles calculations to demonstrate an extra‑electron induced covalent strengthening mechanism and to generalize a ductile‑to‑brittle criterion in a universal hyperbolic form that combines Pettifor's Cauchy pressure with Pugh's modulus ratio for cubic materials. The mechanism involves adding extra‑valence electrons to the parent material matrix, which modifies chemical bonding and strengthens the lattice through covalent interactions. The study shows that Pugh's modulus ratio correlates with hardness and provides insight into the intrinsic brittleness of quasicrystals and bulk metallic glasses.

Abstract

Abstract Traditional strengthening ways, such as strain, precipitation and solid-solution, come into effect by pinning the motion of dislocation. Here, through first-principles calculations we report on an extra-electron induced covalent strengthening mechanism, which alters chemical bonding upon the introduction of extra-valence electrons in the matrix of parent materials. It is responsible for the brittle and high-strength properties of Al 12 W-type compounds featured by the typical fivefold icosahedral cages, which are common for quasicrystals and bulk metallic glasses (BMGs). In combination with this mechanism, we generalize ductile-to-brittle criterion in a universal hyperbolic form by integrating the classical Pettifor's Cauchy pressure with Pugh's modulus ratio for a wide variety of materials with cubic lattices. This study provides compelling evidence to correlate Pugh's modulus ratio with hardness of materials and may have implication for understanding the intrinsic brittleness of quasicrystals and BMGs.