Microstructure and morphology of high temperature oxidation in superalloys

High temperature oxidation in two superalloys has been studied using optica l and scanning electron microscopical techniques. The main applications of superalloys include aircraft turbine blades to heat exchanger tubings for n uclear 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 degrees C, respectively in air. The energy dispersive spectroscopy (EDS) a nd fine-probe linescan microanalysis and X-ray mapping revealed diffusion o f the elements across the metal and oxide regions. Preferential internal ox idation and the role of structural defects were investigated including a co mparison of oxide precipitates grown within and at the grain boundaries of both the alloys. The effect of microstructure on the formation of voids, in ternal and external oxide was examined to elucidate the mechanism of high t emperature oxidation in the alloys. In conclusion, Incoloy 800H exhibited h igher resistance to oxidation as compared to Incoloy 825. (C) 1999 Elsevier Science S.A. All rights reserved.