Characterisation of thermo-mechanical properties of MgO–Al2O3–SiO2 glass ceramic with different heat treatment temperatures

The effects of heat treatment temperature on crystallisation behaviour, precipitated phases and thermo-mechanical properties of some MgO–Al₂O₃–SiO₂ (MAS) glass-ceramics were investigated. Crystallisation behaviour of MgO–Al₂O₃–SiO₂ glasses in the presence of TiO2 as a nucleation agent was studied. The crystalline phases present in the heat treated samples were identified by X-ray diffraction (XRD). It was observed from XRD studies that magnesium aluminium titanate initially precipitated and when the heat treatment temperature was increased to 1140 °C, depending on the thermal history, either magnesium silicate, aluminium titanate and quartz or magnesium aluminium titanate, magnesium aluminate and quartz were precipitated. SEM observation revealed that the heat treatment led to phase separation of droplet-shaped crystals before the needle-shaped crystals formed at 1140 °C. The effect of annealing temperature on the density and mechanical properties of these glass-ceramic were characterised by nanoindentation and the results revealed a significant increase in hardness of the fully crystallised system.