Crystallization and mechanical properties of MgO/Al2O3/SiO2/ZrO2 glass-ceramics with and without the addition of yttria

Glasses in the system of MgO/Al2O3/SiO2 were melted using yttria stabilized tetragonal zirconia or monoclinic zirconia as nucleation agent. In some of them, MgO was partially replaced by ZnO. After melting and casting the glasses, the samples were annealed in the temperature range from 950 to 1150 °C. The obtained glass-ceramics were colourless and transparent to opaque. This is in contrast to glass-ceramics doped with titania or a mixture of titania and zirconia which appear purple to blue. In compositions using 4 mol% tetragonal zirconia stabilized with 3 mol% yttria only β-quartz solid solution was detected. Using monoclinic zirconia or doped zirconia with concentrations >4 mol% resulted in the formation of α-quartz solid solutions. Additionally the crystal phases spinel or gahnite/spinel–solid solution were formed. The formation of these crystal phases also leads to improved mechanical properties. Bending strengths up to 475 MPa, Young’s moduli up to 131 GPa, Vickers hardness up to 12.5 GPa and fracture toughness up to 2.3 MPa m1/2 were obtained.

Glasses in the system MgO/Al2O3/SiO2 were thermally annealed. The addition of zirconia led to the precipitation of small quartz crystals. Small concentrations of yttria notably affected the phases formed.Figure optionsDownload as PowerPoint slide