Temperature–dependent dynamic plasticity of micro-scale fused silica
Remo N. Widmer, Alexander Groetsch, Guillaume Kermouche, Ana Díaz, Gilles Pillonel, Manish Jain, Rajaprakash Ramachandramoorthy, László Pethő, Jakob Schwiedrzik, Johann Michler
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.