Microstructure, chemical aspects, and mechanical properties of TiB_2/Si_3N_4 and TiN/Si_3N_4 composites

The chemical stability of TiB 2 and TiN in a silicon nitride matrix under various conditions of temperature and gaseous environments was investigated. The addition of TiB 2 and TiN on the microstructure and mechanical properties was also studied. No trace of interactions between TiN and Si 3 N 4 was noticed. The addition of TiB 2 to Si 3 N 4 enhanced conversion of the α to β phase of the Si 3 N 4 matrix. Observations of BN and TiN indicated a possible reaction between TiB 2 and Si 3 N 4 . The fracture toughness of Si 3 N 4 was substantially enhanced with the addition of TiB 2 or TiN, while the strength was decreased. Crack deflection was the major toughening mechanism in a Si 3 N 4 /TiB 2 composite. Most of the microcracks passed through TiN particles and cleavaged along preferred orientations with large deflection angles.

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