Coating and spark plasma sintering of nano-sized TiN on Y-α-sialon

TiN coating on Y-α-sialon was accomplished by depositing TiO2 on their particle surfaces through controlled hydrolysis of TiCl4 and Ti(O-i-C3H7)4 and subsequent nitridation with NH3 gas at 1000 °C. TiN particles covering Y-α-sialon were about 20 nm in size. Spark plasma sintering (SPS) of TiN/Y-α-sialon particles produced composite ceramics with continuous TiN networks at 1400 °C, but with TiN grains isolated in elongated β-sialon grains at 1600 °C. The relative density and Vickers hardness of TiN/sialon ceramics SPSed at 1400–1600 °C containing 25 vol.% TiN were measured. The electrical resistivity was in a wide range of 10−4 to 100 Ω cm for the ceramics sintered at 1400 °C, but lowered to the order of magnitude of 10−1 and 105 Ω cm at higher temperatures ≥1500 °C. It was found that the complete transition to β-sialon increased the resistivity to 103 to 105 Ω cm, due to breaking up continuous TiN layers by elongated β-sialon grains.