Microstructure of Si₃N₄-TiN-SiC ceramics during combustion synthesis process

Si₃N₄-TiN-SiC multiphase ceramics were synthesized from TiSi₂ and SiC powders by combustion synthesis. In order to study the combustion process of the TiSi₂-SiC-N₂ system in details, the reaction was stopped at different stages by quenching the samples. The composition and microstructure in different reaction zones were analyzed by X-ray diffraction and scanning electron microscopy. The results show that the main phase of product after complete reaction is whisker-like Si₃N₄, others are TiN and SiC During the combustion synthesis, TiSi₂ particles melt and enwrap on the surface of SiC particles first. As a result, the contact area of TiSi₂ and N₂ increases, and TiN and Si are formed after the reaction. The mid-product, silicon melts or evaporates under high combustion temperature. At the same time, liquid free silicon and unreacted TiSi₂ are completely miscible. Finally, free silicon reacts with nitrogen to form Si₃N₄ crystal nuclei and grow up. Si₃N₄ whiskers are formed during the combustion reaction as a result of the combined effect of vapor-liquid-solid, vapor-solid and evaporation-agglomeration mechanisms.