High-temperature oxidation behavior of SiO2 protective layer deposited on IN738LC superalloy by combustion CVD (CCVD)

A SiO2 protective coating was deposited on an IN738LC alloy using CCVD. The physical properties of a SiO2 protective layer are influenced by the amount of tetraethyl orthosilicate (TEOS, C8H20O4Si). Therefore, the SiO2 protective coating was deposited using different TEOS concentrations and deposition times to optimize the conditions. The deposited coating layer was confirmed to be a SiO2 layer by SEM, EDX, and ESCA analyses. The oxidation resistance of the alloy was evaluated by thermo gravimetric analysis. The oxidation resistance of the SiO2 protective coating was highest when the coating was processed at a TEOS concentration of 0.05 mol/l, which is the highest concentration of source material used. The surface roughness of the SiO2 protective layer also increased with increasing TEOS concentration. The surface roughness of the coating had little effect on the oxidation resistance for a film thickness of approximately 1 μm.