Microstructure, chemical aspects, and mechanical properties of TiB₂/Si₃N₄ and TiN/Si₃N₄ composites

The chemical stability of TiB₂ and TiN in a silicon nitride matrix under various conditions of temperature and gaseous environments was investigated. The addition of TiB₂ and TiN on the microstructure and mechanical properties was also studied. No trace of interactions between TiN and Si₃N₄ was noticed. The addition of TiB₂ to Si₃N₄ enhanced conversion of the α to β phase of the Si₃N₄ matrix. Observations of BN and TiN indicated a possible reaction between TiB₂ and Si₃N₄. The fracture toughness of Si₃N₄ was substantially enhanced with the addition of TiB₂ or TiN, while the strength was decreased. Crack deflection was the major toughening mechanism in a Si₃N₄/TiB₂ composite. Most of the microcracks passed through TiN particles and cleavaged along preferred orientations with large deflection angles.