Interface-mediated softening and deformation mechanics in amorphous/ amorphous nanolaminates

TL;DR

This study investigates how interfaces in amorphous Ta₂O₅/SiO₂ nanolaminates influence their mechanical properties, revealing that interface density affects hardness, deformation mechanisms, and failure modes, differing from crystalline systems.

Contribution

It provides new insights into the deformation mechanics of amorphous nanolaminates, highlighting the role of interface-mediated strain accommodation and shear band behavior.

Findings

Hardness decreases with decreasing bilayer thickness.

Finer bilayer spacings promote closely spaced shear bands.

Interfaces facilitate strain accommodation, preventing catastrophic failure.

Abstract

Interfaces govern the unique mechanical response of amorphous multilayers. Here, we examine nanoindentation hardness and deformation behaviour of amorphous-amorphous Ta$_2$O$_5$/SiO$_2$ nanolaminates with bilayer thicknesses ranging from 2 nm to 334 nm. Whilst monolithic SiO$_2$ exhibits catastrophic failure through a single dominant shear band, multilayer architectures demonstrate varied deformation mechanisms. Hardness decreases with reduced bilayer thickness, from 7.7 GPa at 334 nm to 5.5 GPa at 2 nm spacing, contrasting with crystalline systems, which strengthen with decreasing spacing. Cross-sectional transmission electron microscopy reveals that fine bilayer spacings promote closely spaced vertical shear bands with bilayer compression, while coarser spacings show fewer, widely spaced shear bands with chemical intermixing. Scanning electron diffraction mapping demonstrates significant densification beneath indents. The high interface density facilitates strain accommodation that prevents catastrophic failure typical of brittle amorphous materials.