熔融渗透工艺制备SiC-TiSi2复相陶瓷的反应机理

熔融Si渗透过程伴随着复杂的化学反应及多组分扩散,对该过程进行研究有助于更好地理解熔渗反应机理。本工作采用熔融渗透工艺制备SiC-TiSi2复相陶瓷,在生成SiC基体的同时原位生成TiSi2。通过扫描电子显微镜(SEM)、X射线能谱分析(EDS)和微区X射线衍射(micro-beam XRD)分别对熔融硅区域、Si/SiC界面以及SiC基体的微观结构和相组成进行表征和分析,研究了熔渗工艺制备SiC-TiSi2的反应机理。结果表明:高温下液Si渗入C-TiC预制体,发生化学反应生成SiC、TiSi2以及少量副产物Ti5Si3,其中Ti5Si3主要集中于Si/SiC界面处。随着反应进行,液Si与TiSi2形成液态Ti-Si共晶。该液态共晶通过流动扩散在Si区域中析出TiSi2。而预制体中的少量固态C在液Si中溶解、扩散,并在Si区域生成均匀分布的孤立SiC颗粒。

Reaction mechanism of SiC-TiSi2 by melt infiltration method

The melt infiltration method is one of the main preparation method of SiC matrix composites. Complex reactions and multi-component diffusion are involved in molten-Si infiltration of a C-based preform. In this study, SiC-TiSi2 was fabricated by Si melt infiltration and the TiSi2 was in-situ formed in the matrix of SiC. In order to explore the reaction mechanism of SiC-TiSi2, SEM, EDS and micro-beam XRD were determined to characterize the phase constitute and micro-structure in different regions along the Si melt infiltration direction. The results demonstrate that SiC, TiSi2 and Ti5Si3 which concentrate on the Si/SiC interface are found to be formed through the Si melt infiltration into the C-TiC preform. With the increase of temperature, the liquid phase of Ti-Si appears when exceeding the Si-TiSi2 eutectic temperature. And the liquid Ti-Si eutectic precipitates TiSi2 in the Si region during the cooling period of the sample. Moreover, the isolated SiC grain in Si region is produced by the precipitation from the dissolution of solid C in liquid Si.