Surface oxidation of Al-Cr-Fe alloys characterized by X-ray photoelectron spectroscopy

We present X-ray photoelectron spectroscopy (XPS) measurements of several A l-Cr-Fe samples which are mixtures of approximants of the decagonal phase. Some samples also contain a hexagonal gamma -brass phase. Our purpose is to evaluate the effect of chemical composition, particularly Cr content, on t he response of the surface to oxidation. Under mild conditions only alumini um oxidizes, but under extreme conditions (water immersion at room temperat ure, or oxygen exposure at high temperatures), chromium oxidizes as well. X PS data also provide a measure of the oxide thickness. Cr has no discernibl e effect on oxide thickness when the oxidizing environment is the gas phase , but provides significant protection against water immersion, where high c oncentrations of Cr reduce the thickness by as much as 40%. These results f or the Al-Cr-Fe samples are compared with results for approximants and quas icrystals in other systems. (C) 2001 Elsevier Science B.V. All rights reser ved.