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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]

This work was aimed at reporting a new method for fabrication of TaSi 2 coating. In this research, vacuum plasma spray (VPS) process was applied to fabricate TaSi 2 coating. The chemical composition and microstructure of the coating was characterized by SEM, XRD, TEM and EDS. Its thermal stability was evaluated by TG-DTA and oxidation tests at 500 °C–1000 °C. The results showed that the TaSi 2 coating was composed of hexagonal TaSi 2 phase and presented dense lamellar microstructure combining defects, such as pores, interfaces and oxygen impurity. There was a sharp weight increase in TG curve at range of 800 °C–1000 °C with an exothermic phenomenon. The coating exhibited excellent thermal stability at 500 °C up to 50 h in atmospheric environment. Obvious oxidation was observed at 800 °C. The TaSi 2 coating was completely oxidized and fragmented into pieces after oxidation at 900 °C for 1 h. The oxidation mechanism was also discussed. [ABSTRACT FROM AUTHOR]