Crystalline phase formation, microstructure and mechanical properties of a lithium disilicate glass–ceramic

In this work, crystalline phase formation, microstructure and mechanical properties of a lithium disilicate (LS2, Li2Si2O5) glass–ceramic in the SiO2–Li2O–Al2O3–P2O5 system were investigated. A four-stage heat treatment process was used for crystallization of the glass. The effects of holding time and temperature at the final stage on the crystalline morphology of the glass–ceramic were studied. The experimental results revealed the two crystallization peaks at 672 and 839 °C. At a temperature lower than 770 °C and holding time of 20 min, the lithium metasilicate (Li2SiO3) phase dominates. On the other hand, when the glass was heated to a higher temperature or held for a longer time, the LS2 phase dominates and some other minor phases such as cristobalite and lithium phosphate emerge. Scanning electron microscopy and energy dispersive spectrometry revealed a large number of nanosized ZrO2 particles when the crystallization temperature was above 790 °C. Vickers hardness of the LS2 glass–ceramic was about 8.1–8.4 GPa and flexural strength was in the range of 282–307 MPa. Crack deflection was observed along the LS2 cluster boundaries. The crystallization sequence was proposed to explain the observed microstructure and phases.