Microstructure Characteristics and Oxidation Behavior of Molybdenum Disilicide Coatings Prepared by Low Pressure Plasma Spraying

Molybdenum disilicide (MoSi₂) has been applied as protective coating material on various substrates fabricated by different methods due to its good oxidation resistance at elevated temperature, relatively low density and coefficient of thermal expansion and high thermal conductivity. In this work, MoSi₂ coatings were fabricated by low pressure plasma spraying technology (LPPS). Their morphology, composition and microstructure characteristics were intensively investigated by SEM, XRD, EDS and TEM. The oxidation behaviors of MoSi₂ coatings were also explored. The results showed that the MoSi₂ coating was compact with porosity less than 5%. Its microstructure exhibited typical lamellar character. The MoSi₂ coating was made up of grains with irregular shapes and different sizes of 0.1-0.2 µm. It was mainly composed of tetragonal and hexagonal MoSi₂ phases. A small amount of tetragonal Mo₅Si₃ phase formed and randomly distributed in the matrix of MoSi₂. The MoSi₂ coating exhibited excellent oxidation-resistant behavior at 1773K, which resulted from the continuous dense glassy SiO₂ film formed on its surface.