Optimization of microstructure and properties of in situ formed β-O-sialon–TiN composite

A powder mixture of α-Si3N4, Al2O3, and TiO2 was hot-pressed using different sintering cycles to search for an optimum in situ formed β-O-sialon–TiN composite. The impulse excitation technique (IET), high-temperature X-ray diffraction (HTXRD), and scanning electron microscopy (SEM) were used to investigate the microstructure. Below the temperature of 1300 °C, the high-temperature internal friction (Q−1) decreases with the increase of sintering temperature, whereas the density of the material increases with the increase of sintering temperature. At a sintering temperature higher than 1850 °C, the ceramic could not be densified and O-sialon was not formed. Also, the mechanical properties of ceramics hot-pressed using different sintering cycles were assessed. The ceramic hot-pressed at 1700 °C for 10 min displays a combination of high hardness and good fracture toughness, due to an optimum combination of β-sialon, O-sialon, and TiN-phases. This paper also evaluated the thermal expansion of β-sialon in the different ceramics hot-pressed using different sintering cycles.