Effect of heating rate on microstructure and properties of spark plasma sintered Li-α-sialon

Li-α-sialon ceramics with low oxygen content were prepared by spark plasma sintering at 1750 °C, using three heating rates of 100 °C/min, 200 °C/min and 300 °C/min. In all cases, the densification of Li-α-sialon ceramics is effectively promoted. The rapidly anisotropic growth of grains, either α-sialon or β-sialon, is significantly enhanced with a heating rate above 200 °C/min. This could be attributed to a large amount of low viscosity oxygen-rich liquid formed at elevated temperatures, which gives rise to a so-called dynamic ripening mechanism at the early stage of sintering. Furthermore, for the composition near α-sialon boundary, the oxygen-rich liquid results in the formation of β-sialon together with a large amount of intergranular glassy phase. Only the Li-doped sialon with low lithium and oxygen content possesses relatively high infrared transmittance when sintered at a rate of 100 °C/min.