Mechanical properties of ion-exchanged alkali aluminosilicate glass

Abstract

Aluminosilicate glasses present good optical and mechanical properties, but their mechanical behavior can be further improved by thermal or chemical treatments, making them suitable for applications requiring high hardness and fracture strength, for example, laptop monitors or mobile phone screens. A lithium aluminosilicate composition was prepared, and ion exchanged in a KNO₃ bath at different temperatures for various times. Density and UV–vis transmission were measured before and after ion exchange of the glass, together with the mechanical properties, namely, Young's modulus, Poisson's ratio, shear modulus, Vickers hardness, indentation fracture toughness, and equi-biaxial bending strength, whose results were treated by Weibull statistics. The initial glass composition presented a Vickers hardness of 620 ± 10 HV, a Young's modulus of 87 ± 1 GPa, and a fracture toughness of 1.7 ± .1 MPa.m^1/2. After ion exchange, the Vickers hardness of the glass increased to average values of 716 HV for 12 h at 450°C and 728 HV for 30 h at 420°C, while the fracture toughness increased to 2.2 ± .1 MPa.m^1/2, confirming the improvement of the mechanical properties. These results have been compared with two commercial glasses: a monitor glass from a laptop computer and a glass normally used in mobile phone screens.