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Abstract
Oxidation and corrosion properties at 900°C of two coatings, one containing platinum and the other platinum-free, on IN792 were investigated. During the corrosion exposures, sodium sulfate salt was situated in the furnace together with the coated specimens. The temperature of the salt was kept above its melting point but lower than the temperature of the coating i.e. 900°C. The exposure times ranged from 100 to 1000 h. The formed oxide scales were studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and scanning transmission electron microscopy techniques. It is shown that the presence of Pt improves the protective properties of the coating against corrosion. The propagation stage of corrosion on the platinum-free coating is reached already after 100 h of exposure. On the other hand the scale formed on the platinum-rich samples still appeared to be protective even after 500 h. The details concerning structure and chemistry of the scales formed are presented and discussed.