Regulation of phase evolution of CaAl12O19 on properties of in-situ formed MgAl2O4–CaAl12O19 composites

The in-situ formed MgAl 2 O 4 –CaAl 12 O 19 (MA–CA 6 ) composites were fabricated in this study. To clarify the influence of the evolution of CA 6 phase on the properties of MA–CA 6 composites, the sintering temperature was carried out at 1200–1700 °C for 2 h. The results show that the growth and development of CA 6 grains improves the densification and flexural strength of MA–CA 6 composites. The formation of MA phase occurs at 1200 °C, while the CA 6 phase is formed by the reaction of CaAl 4 O 7 (CA 2 ) and Al 2 O 3 appears at 1400 °C. The plate-like CA 6 grains intersect with each other, presenting regular hexagonal morphology with a high aspect ratio at 1500 °C. The CaO–Al 2 O 3 –SiO 2 phase acts as an interface phase to regulate the growth and development of MA and CA 6 grains. The CA 6 phase was crystallized from the transient liquid phase CaO–Al 2 O 3 –SiO 2 to significantly increase its thickness at 1600 °C. At the same time, as the sintering temperature rises, the apparent porosity of the sample decreases from 24% at 1400 °C to 4% at 1600 °C, and the flexural strength correspondingly increases from 96.6 MPa to 167 MPa. However, the suitable sintering temperature should not exceed 1600 °C for better properties of the composites.