Effect of zirconium concentration on nodule formation during cyclic oxidation of Fe-15Cr-4Al alloy at 1300 degree C

The effect of small concentrations of zirconium on the cyclic oxidation behavior of Fe-15Cr-4Al was investigated at 1300 degree C. The zirconium concentrations studied were 0.2, 0.55, and 1 wt.%. Each cycle consisted of a 1-hr isothermal period followed by 30-min cooling of the sample in air. Nodule formation was observed in higher zirconium-containing alloys, 0.55% and 1% zirconium, and the base alloy. The nodules formed at the corners and edges of the specimen and grew with increasing number of cycles. EDAX and line scans of cross section of oxidized samples demonstrated that the nodules were composed of iron oxides. Suggestions are given regarding the mode of nodule formation. Results show that additions of 0.2% zirconium and 1% yttrium to the base alloy suppress the nodule formation and provide the best resistance to cyclic oxidation