The growth of MoSi2 films by the electrochemical siliciding of Mo was investigated and MoSi2 film formation was attempted on a Ni-based superalloy (CMSX-4) via a two-step coating process. An oxidation test of the MoSi2 film was also performed. A thick MoSi2 film was obtained at a temperature below 1073 K. At a relatively high current density of 100 mA · cm-2, the supply of Si to the Mo surface was too fast and pure Si was deposited outward instead of alloying. The growth rate of MoSi2 at 50 mA · cm-2 was 57 μm · h-1, abnormally fast compared to that by normal diffusion. This indicated that Si diffused through the grain boundaries, rather than through grain bodies. A dense and homogeneous MoSi2 film, approximately 100 μm thick, was successfully formed on CMSX-4. The boundaries in MoSi2/Mo and Mo/CMSX-4 were coherent. After oxidation testing, a multilayer comprising SiO2, MoSi2, Mo5Si3, Mo, an intermediate layer, and CMSX-4 was formed. The SiO2 film was significantly thick at 10-30 μm compared to literature values. To obtain a thin SiO2 film, a MoSi2 layer with fewer defects might be required.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry