Visualizing and Quantifying Indentation-Induced Densification and Cracking in Vitreous Silica.

The practical strength of oxide glasses is greatly reduced by surface flaws that form during processing and use. Instrumented indentation can mimic such real-life damage events and allows for systematic examination of the deformation and structural changes in the regions of the glass being indented. However, structural probing is nearly always performed after rather than during the sharp contact event, limiting our understanding of the indentation process. To overcome this, here we develop and apply an in situ nanofocus X‑ray scattering method for visualizing and quantifying indentation-induced densification and cracking in glass materials. We demonstrate its feasibility in a proof-of-concept experiment by probing the local mechanical and structural response of vitreous silica during indentation. Two-dimensional mapping of the scattering pattern in the zone below a sharp diamond wedge indenter reveals local changes in the atomic structure and density as well as cracking behavior. These in situ measurements during indentation reveal the formation and evolution of the densification zone and cracking, probing features down to the nanoscale. Although the developed experimental approach can be further improved (especially beam-sample-indenter alignment), we believe it will allow for a deeper understanding of the interplay between structural densification and cracking behavior in glasses.