Crack initiation behavior of sodium aluminosilicate glasses

Crack initiation behavior of sodium aluminosilicate glasses has been investigated by using Vickers indentation and scratch techniques. Compositional variation of the crack initiation behavior has been discussed in terms of the elastic and inelastic mechanical responses of the glasses. Vickers hardness and Young's modulus increase with increasing the ratio of Al2O3 to Na2O in glass. As for the crack initiation behavior, the addition of Al2O3 to Na2O-SiO2 glass causes an increase in the crack forming probability and a decrease in the crack initiation load. No maximum or minimum is found in the compositional variation of crack initiation behavior. This means that the crack initiation process can be affected not by the alkali mobility but by the rigidity of glass network. The addition of Al2O3 to Na2O-SiO2 glass causes the reduction of the number of non-bridging oxygens and the increase in rigidity of glass network at the Al2O3/Na2O < 1. At the ratio > 1, it is assumed that the formation of O(Al2Si) or O(AlSi2) triclusters also increases the rigidity of glass network. It is concluded that a decreased ability to deform leads to easy crack initiation in Na2O-Al2O3-SiO2 glasses with higher Al2O3 content. (C) 2004 Elsevier B.V. All rights reserved.