Effect of TiO2 content on the crystallization behavior and properties of CaO-Al2O3-SiO2 glass ceramic fillers for high temperature joining application.

The effects of TiO 2 content on the crystallization behavior, microstructure, microhardness, coefficient of thermal expansion (CTE) and softening temperature of CaO-Al 2 O 3 -SiO 2 glass ceramic fillers were investigated. The results show that the crystallization activation energy (E) firstly decreases and then increases with the TiO 2 addition from 10 wt% to 20 wt%. The microstructure and phase composition of glass ceramics importantly depend on the content of TiO 2 . Low TiO 2 content results in formation of Ti-contained crystals (CaTiSiO 5 ) due to phase separation. In contrast, high TiO 2 concentrations lead to precipitation of small titanium oxide crystals that act as nuclei, facilitating the development of CaAl 2 Si 2 O 8 . Furthermore, the formation of crystalline phases is beneficial for improving the microhardness and refractoriness of glass ceramics. The CaO-Al 2 O 3 -SiO 2 glass with 15 wt% TiO 2 addition exhibits the highest crystalline volume fraction possibly due to the lowest activation energy of crystallization. As a result, its microhardness and softening temperature can reach as high as 898.2 HV and 1027 °C, respectively. However, its CTE slightly decreases from 7.44 × 10 −6 /°C to 6.35 × 10 −6 /°C after crystallization treatment because of the formation of CaTiSiO 5 . [ABSTRACT FROM AUTHOR]