Microstructure and morphology of high temperature oxidation in superalloys

High temperature oxidation in two superalloys has been studied using optical and scanning electron microscopical techniques. The main applications of superalloys include aircraft turbine blades to heat exchanger tubings for nuclear reactors. The present investigation deals with a comparison of high temperature oxidation behaviour in two superalloys. The morphology of oxide growth in the specimens was examined in specimens exposed at 1000 and 1200°C, respectively in air. The energy dispersive spectroscopy (EDS) and fine-probe linescan microanalysis and X-ray mapping revealed diffusion of the elements across the metal and oxide regions. Preferential internal oxidation and the role of structural defects were investigated including a comparison of oxide precipitates grown within and at the grain boundaries of both the alloys. The effect of microstructure on the formation of voids, internal and external oxide was examined to elucidate the mechanism of high temperature oxidation in the alloys. In conclusion, Incoloy 800H exhibited higher resistance to oxidation as compared to Incoloy 825.