The oxidation of thin foils of FeCrAl(RE) alloys in moist air

The effect of varying levels of water vapour in air on the oxidation of FeCrAl plus Reactive Element (RE) alloys has been investigated at temperatures of 1200 degreesC and 1300 degreesC. Thin (<125 <mu>m) foils of three different commercial alloys (Kanthal AT, PM2000 and Aluchrom YHf) have been tested to failure in laboratory air and air containing 3.2 vol.% water vapour. At this point th. protective aluminium oxide scale fails and the alloys go into breakaway oxidation with the formation of chromium- and then iron-rich oxide. Our results would suggest that high levels of water vapour in the atmosphere speed up the initial oxidation and reduce the overall lifetime of the thin components. The important factor for the total scale failure, the formation of non-protective iron oxide, is the depletion of Al levels to a critical value, below which no protective alumina scale can form; and this occurred slightly faster in an air + 3.2 vol.% water vapour environment.