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 alpha to beta 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.