Role of elastic deformation in determining the mixed alkaline earth effect of hardness in silicate glasses

Glasses deform permanently as a result of indentation and the total resistance to deformation consists of three individual resistances, i.e., those to elastic deformation, densification, and plastic flow. The link between Vickers hardness and the resistances to densification and plastic flow has been investigated previously, but the link between the resistance to elastic deformation and hardness has not yet been studied. In this work, we investigate the link between elastic deformation during indentation and Vickers hardness in a series of mixed magnesium-barium boroaluminosilicate glasses. We show that the mixed alkaline earth effect manifests itself as deviations from linearity in shear modulus, Poisson’s ratio, glass transition temperature, liquid fragility index, hardness, volume of densification, and volume of plastic flow. We find no correlation between the elastic part of the indentation and hardness, and we thus infer that elastic deformation does not play a dominant role in determining the mixed alkaline earth effect of hardness. However, interestingly, we find a
strong correlation between Poisson’s ratio, volume of plastic flow, and hardness, by which the minimum in hardness could be explained in terms of a minimum in shear viscosity