Effect of Sintering Temperature on Microstructure and Properties of TiN Ceramics by Pressureless Liquid Phase Sintering

TiN ceramics were prepared by pressureless liquid phase sintering with micron TiN powder as raw material and nano Y₂O₃ and Al₂O₃ powders as liquid phase sintering additives. The effect of sintering temperatures (1 700–1 850 ℃) on the microstructure, mechanical properties and electrical properties of TiN ceramics was studied. The results show that the ceramics consisted of TiN, YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉) phases at different sintering temperatures. When the sintering temperature was lower than 1 800 ℃, TiN phase was distributed evenly, and the content of YAG and YAM phases was low. When the sintering temperature was 1 800 ℃, TiN grains grew up, and the content of YAG and YAM phases increased. The relative density, Vickers hardness, flexural strength and fracture toughness of TiN ceramics all increased first and then decreased with the increase of sintering temperature, while open porosity and resistivity both decreased first and then increased. The fracture mode of the ceramics was mainly intergranular fracture when the sintering temperature was lower than 1 800 ℃, and was mainly transgranular fracture when the sintering temperature was not lower than 1 800 ℃. The TiN ceramics sintered at 1 800 ℃ had the best comprehensive properties with the highest relative density, Vickers hardness, flexural strength and fracture toughness, which were 98.3%, 13 GPa, 420 MPa, 6.1 MPa · m^1/2, respectively, and the lowest open porosity and resistivity, which were 0.12% and 3.04×10⁻⁷ Ω · m, respectively.