Microalloying and the mechanical properties of amorphous solids

TL;DR

This paper provides a theoretical framework explaining how microalloying elements influence the mechanical properties of amorphous solids by creating defects that affect shear moduli and plastic responses, thereby enhancing ductility and yield strain.

Contribution

It introduces a theory linking microalloying-induced local structural changes to macroscopic mechanical property improvements in amorphous solids.

Findings

Microalloying elements form isotropic defects that modify shear moduli.

Defects interact with plastic responses, affecting shear band formation.

Theory predicts increased yield strain and estimates nano-shear band lengths.

Abstract

The mechanical properties of amorphous solids like metallic glasses can be dramatically changed by adding small concentrations (as low as 0.1\%) of foreign elements. The glass-forming-ability, the ductility, the yield stress and the elastic moduli can all be greatly effected. This paper presents theoretical considerations with the aim of explaining the magnitude of these changes in light of the small concentrations involved. The theory is built around the experimental evidence that the microalloying elements organize around them a neighborhood that differs from both the crystalline and the glassy phases of the material in the absence of the additional elements. These regions act as {\em isotropic} defects that in unstressed systems dress the shear moduli. When strained, these defects interact with the incipient plastic responses which are quadrupolar in nature. It will be shown that this interaction interferes with the creation of system-spanning shear bands and increases the yield strain. We offer experimentally testable estimates of the lengths of nano-shear bands in the presence of the additional elements.