燃烧合成制备Si3N4-TiN-SiC陶瓷的显微结构

以TiSi2为反应原料,SiC作稀释剂,燃烧合成制备Si3N4-TiN-SiC陶瓷.利用燃烧波"淬熄"法使反应各个阶段的物相得以保留,通过X射线衍射及扫描电镜分析TiSi2在燃烧合成中的反应过程及显微组织转化.结果表明:完全反应后产物的主相为Si3N4,其余为TiN和SiC.在燃烧过程中,TiSi2首先受热熔化,包覆于SiC颗粒表面,随后与N2反应生成TiN和Si.Si在高热作用下发生熔化、汽化,液态Si与未反应的TiSi2互溶.生成的Si与氮气发生反应,形成Si3N4晶核,并不断长大.燃烧合成反应过程中,Si3N4晶须的生长十分复杂,由气-液-固机制、气-固机制及蒸发凝聚的气相生长机制共同作用.

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.