Effect of diamond doping on carbothermal reduction reaction and properties of Si3N4 ceramics

Si ₃ N ₄ ceramics were sintered at 1900℃ for 12 h with Y ₂ O ₃ and MgSiN ₂ as sintering aids under 1 MPa nitrogen pressure. The effects of diamond with different particle sizes (1,2 μm) as carbon source on the microstructure, thermal properties and carbothermal reduction behavior of Si ₃ N ₄ ceramics were systematically studied. The results show that the carbothermal reduction process introduced by diamond significantly reduces the oxygen content and increases the N/O ratio of the secondary phase at the grain boundary. Among them, the sample with 1μm diamond (SNC-1) showed the best reaction efficiency: the fine-grained diamond had a higher specific surface area and stronger reactivity, which promoted the uniform carbothermal reduction reaction and effectively removed the oxygen impurities at the grain boundary. In the final dense Si ₃ N ₄ ceramics, although the strength of the SNC-1 sample with 1 μm diamond is slightly sacrificed, with the decrease of grain boundary oxygen content, the content of β-Si ₃ N ₄ increases, the grain morphology develops into a rod shape and the size is obviously coarsened, forming a microstructure that is more conducive to heat conduction. Therefore, SNC-1 achieves a balance between thermal conductivity and mechanical properties, and improves thermal conductivity while maintaining high strength. This is of great significance for the application scenarios that pursue the synergy of high thermal conductivity and good mechanical properties.