Thermal history dependence of indentation induced densification in an aluminosilicate glass

• We study the dependence of indentation induced densification on thermal history.
• As fictive temperature Tf increases the resistance to densification decreases.
• It is more difficult to initiate radial cracks in glasses showing larger densification.
• The extent of the indentation size effect increases with decreasing Tf.

The mechanical properties of glasses are not only determined by their chemical composition, but also by their thermal history, i.e., fictive temperature. In this paper, we consider an alkaline earth aluminosilicate glass composition which has been annealed to exhibit a wide range of fictive temperatures (~ 130 K). Hardness and brittleness index have previously been shown to increase with decreasing fictive temperature, whereas the crack resistance decreases. Through quantification of the indentation depth before and after heat treatments, we show that these changes in micromechanical properties arise from an increased resistance to densification under the indenter when the glasses are annealed. We discuss these results in relation to the indentation size effect and the overall network compaction.