Temperature–dependent dynamic plasticity of micro-scale fused silica

Abstract

The ability to predict the micro-scale strength and plasticity of fused-silica micro-components is crucial as their miniaturization and applications in harsh environments advance. This study focusses on the micro-mechanical behavior of fused silica micropillars at high temperatures and variable strain rates. 160 micropillars with a diameter of 1.6 µm have been tested at temperatures between −120 °C and 600 °C and strain rates between 10-3 s−1 and 1 s−1, which are to date unexplored conditions. Between −120 °C and 300 °C, the yield strengths (6–8 GPa) and strain rate sensitivities (≤0.03) vary only marginally. However, at 600 °C, a significant decrease in yield strength by more than 50 % (2.5–4.5 GPa) and an increase in strain rate sensitivity by a factor of 3 (0.09) is observed. Post-compression synchrotron-based ptychographic X-ray computed tomography (PXCT) on plastically deformed micropillars revealed a transition in deformation mechanisms: Shear-localization and shear-promoted densification at 25 °C; homogeneous shear-flow and densification limited by radial cracking at 300 °C; and unconstrained shear-flow and limited densification due to weak confinement strength at 600 °C. FEM results support these observations while separating geometric from material-intrinsic effects. These results suggest that the classification of fused silica as a glass that deforms predominantly through densification should be challenged – at least under unconstrained compression, which is the predominant mode of loading in applications.