Indentation deformation mechanism of isostatically compressed mixed alkali aluminosilicate glasses

Oxide glasses can be permanently densified through application of high pressure at room or elevated temperature. Such treatment allows for modification of macroscopic glass properties. However, the structural origins of the pressure-induced property changes are not yet fully understood. In this study, we investigate the ability of a glass network to resist densification under pressure at both ambient and elevated temperatures. We study the detailed deformation mechanisms (densification and shear flow) that occur during indentation of series of as-prepared and isostatically compressed mixed Na/K aluminosilicate glasses, which exhibit a pronounced nonlinear scaling in glass properties due to the mixed alkali effect. Following pressure treatment at elevated temperature, an increase in Vickers hardness is observed due to a significant decrease in densification under the indenter. In contrast, the volume of glass developed in the pileup regions due to shear flow is unaffected by the pressure treatment. This change in the relative contributions of these plastic deformation mechanisms can explain the decrease in crack resistance of the glasses induced by the isostatic compression treatment.