包渗法制备硅化物涂层的结构形貌及形成机理

采用包渗法在C-103铌合金基体上制备MoSi2涂层，通过X射线衍射、扫描电镜和能谱分析等手段研究涂层表面、截面形貌以及氧化后涂层结构变化，并分析硅化过程中涂层的形成机理。研究结果表明：包渗法制备硅化物涂层是通过反应扩散形成的，硅化过程服从抛物线规律；该涂层为复合结构：MoSi2相为主体层；以NbSi2相为主、并含少量Nb5Si3相的两相为过渡区；Nb5Si3相为扩散层。在高温氧化环境下，涂层表面生成致密的非晶氧化层，有效地阻止了氧向涂层内扩散。

Microstructure and formation mechanism of silicide coating prepared by pack cementation

A MoSi2 coating on C-103 niobium alloy was prepared by packing cementation, and the microstructures of the oxidized and unoxidized coatings were analyzed by XRD, SEM and EDS techniques. The formation mechanism of the silicide coating was investigated. The results show that the silicide coating is formed by reactive diffusion and the silicification process obeys parabolic relation. The coating is composed of composite structures including MoSi2 outer layer, two-phase transient zone with major NbSi2 and minor Nb5Si3, and Nb5Si3 diffusion inner layer. The coating possesses good high-temperature oxidation resistance and spalling resistance. At high temperature and under oxidation circumstance, the dense amorphous glass scale is formed on the coating, which prevents the process of the oxygen diffusion to inner layer.