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.
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