Preparation and Mechanical Properties of Mullite-Ti(C,N) Composites

Mullite-Ti(C,N) composites were synthesized using TiO₂, graphite and Al/Si/Al₂O₃ composite powders as precursors. The samples were subjected to a carbothermal reduction nitridation process at temperatures ranging from 1400 to 1600 ℃ in nitrogen atmosphere for 2 h. The effects of firing temperature on phase composition, microstructure and mechanical properties of the composites were studied. According to X-ray diffraction results, after heat treatment at 1400 ℃, the samples consisted of Ti(C,N), SiO₂ and cristobalite. With increasing firing temperature to 1450–1600 ℃, cristobalite phase disappeared, while short columnar mullite phase is present, which is intimately bonded to amorphous SiO₂, resulting in effective chemical bonding. Furthermore, at 1500 ℃, microstructure and mechanical properties of the composites were significantly improved, including a reduction in the number of open pores and an enhancement in particle bonding. The optimized sample had bulk density, elastic modulus, flexural strength and Vickers hardness to be (3.48±0.02) g·cm⁻³, (138.5±0.1) GPa, (158.0±0.03) MPa and (21.01±0.01) GPa, respectively.