Oxidation behavior of ternary Fe-15Cu-5Al and Fe-85Cu-5Al alloys in pure oxygen at 900 degrees C

The oxidation of two two-phase ternary Fe-Cu-Al alloys containing about 5%(mole fraction) aluminium, one Fe-rich and one Cu-rich, has been studied at 900 degrees C in 1 x 10(5) pa pure oxygen. The Fe-rich Fe-15Cu-5Al alloy presents two quasi-parabolic stages, with a large decrease of the parabolic rate constant after about 50 min. The presence of 5% At greatly reduces the oxidation rate of this alloy with respect to a binary Fe-Cu alloy of similar composition by forming an external protective Al2O3 layer, which is present near the scale/alloy interface. Due to the high stress-growth effect, this thin Al2O3 layer cannot completely prevent further oxidation of the alloy underneath. On the contrary, the Cu-rich Fc-85Cu-5Al alloy presents a single parabolic stage and forms a thick and porous external scale, coupled to the internal oxidation of Fe and Al. As a result, the oxidation of Cu-rich alloy at 900 degrees C is much faster than that of the Fe-rich alloy.