Nanoindentation Study of the Surface of Ion-Exchanged Lithium Silicate Glass

Variations in mechanical properties (stiffness and hardness) were measured as a function of case depth in ion-exchange glasses using nanoindentation. A simple silicate composition, 30Li(2)O-70Si(2)O, was exchanged (Li+ <-> K+) at several different temperatures, below and above the glass transition, to evaluate the effect of exchange temperature on mechanical properties throughout the ion-exchange layer. Significant enhancements in Young's modulus and hardness were found near the edge in ion-exchanged glasses and attributed to compressive stress and the mixed-alkali effect. Indent size effect-like behaviors were observed in the untreated and ion-exchange samples alike near the sample edge; this was explained by surface-condition sensitivity and compressive stress found within this region. The elastic recovery and resistance to plastic deformation were calculated to assess the effect of ion exchange on elastic and plastic mechanical responses. Microhardness measurements of the exchanged samples were also made for comparison.