Influence of TiO2 content on the crystallization and microstructure of machinable glass-ceramics

Glasses based on the SiO2–Al2O3–MgO–K2O–B2O3–MgF2 system added with TiO2 were synthesized and characterized by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. The results showed that by increasing the TiO2 content, glass transition temperature (Tg), both the crystallization peak temperature (TpI and TpII) and activation energy (E) increased. The interconnected large blocky card-like crystals were identified as fluorophlogopite as a major crystalline phase for all three glass-ceramic specimens by (XRD) and subsequently confirmed by SEM. The Vickers hardness (Hv) value for glass-ceramic specimens decreases with progressively increasing TiO2 content (1–10 wt%) and Titania containing MGT-3 glass-ceramic specimen with interconnected large blocky card-like fluorophlogopite mica crystals possess lower Hv (4.26 GPa) as well as good machinability (m = 0.12) useable for machinable applications. The study shows that Titania promoted initial crystallization of glass and can be used as an effective nucleting agent.