Elastic and micromechanical properties of isostatically compressed soda–lime–borate glasses

Isostatic pressure-induced changes in elastic constants and micromechanical properties of soda–lime–borate glasses of molar composition xNa2O⋅10CaO⋅(90 − x)B2O3 with x = 5, 15, and 25 were determined by performing Brillouin scattering and Vickers indentation experiments. An increase of the isostatic pressure up to 570 MPa resulted in an increase of Youngʹs modulus of 19, 11, and 7% and of hardness at 9.81 N load of 33, 22, and 18% for x = 5, 15, and 25, respectively. The decrease in the resistance to crack initiation (ratio of at least 2) and the increase in the crack-to-indent ratio (change > 13%) followed the same compositional trend. Consequently, fracture toughness and brittleness of the soda–lime–borate glasses were negatively and positively correlated with isostatic pressure, respectively. These changes were correlated with the overall decrease of the molar volume.