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

Abstract

The in-situ formed MgAl2O4–CaAl12O19 (MA–CA6) composites were fabricated in this study. To clarify the influence of the evolution of CA6 phase on the properties of MA–CA6 composites, the sintering temperature was carried out at 1200–1700 °C for 2 h. The results show that the growth and development of CA6 grains improves the densification and flexural strength of MA–CA6 composites. The formation of MA phase occurs at 1200 °C, while the CA6 phase is formed by the reaction of CaAl4O7 (CA2) and Al2O3 appears at 1400 °C. The plate-like CA6 grains intersect with each other, presenting regular hexagonal morphology with a high aspect ratio at 1500 °C. The CaO–Al2O3–SiO2 phase acts as an interface phase to regulate the growth and development of MA and CA6 grains. The CA6 phase was crystallized from the transient liquid phase CaO–Al2O3–SiO2 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.