High strength glass–ceramics in the system MgO/Y2O3/Al2O3/SiO2/ZrO2 without quartz as crystalline phase

This paper is the first report on high strength glass–ceramics which mainly contain zirconia as crystalline phase. This is in contrast to previous reports on high strength glass–ceramics which contain low quartz as the crystalline phase. Glasses in the system MgO/Y2O3/Al2O3/SiO2 with zirconia as nucleating agent were melted. The samples were crystallised in a first step at 950 °C for different periods of time and in the second step at 1060 °C for 1 h. The prepared glasses and glass–ceramics were characterised using differential thermal analysis, dilatometry, X-ray diffraction, and scanning electron microscopy. As shown by X-ray diffraction after the first step in every analysed composition, zirconia was precipitated. With increasing crystallisation time and temperature and depending on the composition, the other phases such as β- or α-quartz solid solutions, spinel and indialite were precipitated. With higher yttria concentrations and increasing crystallisation temperatures during the second crystallisation step, the main crystalline phase was zirconia whereas the quartz solid solution was no longer observed. Bending strengths up to 450 MPa and Young′s moduli up to 115 GPa were obtained after the two subsequent crystallisation steps. Higher yttria concentrations resulted in an increase in density and microhardness. The maximum Vickers hardness was 10.5 GPa.