Microstructure Evolution of Plasma-Sprayed MoSi2 Coating at RT-1200 °C in Air.

In this work, the phase composition and microstructure evolution of vacuum plasma-sprayed MoSi2 coating between room temperature and 1200 °C in air was evaluated and characterized. The results showed that hexagonal MoSi2 (h-MoSi2) became the main phase in the deposited coating, which remained even after 50 h oxidation at 500 °C, exhibiting excellent thermal stability. MoO3 bundles and SiO2 clusters were generated by consuming tetragonal MoSi2 (t-MoSi2) after 1 h, and white powders formed on the coating’s surface after 10-h exposure to air at 500 °C. Most h-MoSi2 transformed to t-MoSi2 at 800 °C; moreover, a protective silica layer formed on the coating surface. Similar phenomenon was observed for the coating exposed to 1000 °C where grain growth also occurred. Vacuum heat treatment at 900 °C effectively improved the thermal stability of the MoSi2 coating. The formation of silica layer alleviated negative effects of structural defects and helped the MoSi2 coating serve as a protective coating for varied substrates. [ABSTRACT FROM AUTHOR]