Keiichi Ohmura

EFFECT OF LANTHANOID ON OXIDATION BEHAVIOUR OF Fe-Cr-Al FOIL

Oxidation behaviour of Fe-Cr-Al foil was investigated in relation to the addition of Lanthanoid (Ln) to determine the optimum composition as foil and to discuss the role of Ln. Oxidation life of Ln-free foil depended on the Al content, and breakaway occurred immediately when the all of Al contained in the foil was consumed as Al 2 O 3 . However, with Ln addition, oxidation resistance of foil was remarkably improved, because the scale was more compact and protective by the presence of Ln in the Al 2 O 3 . However, an excessive addition of Ln reduced the oxidation resistance by forming its own oxide in the scale along the grain boundary of substrate as a defect for protective scale. The optimum range of Ln content for the oxidation resistance of a foil exists from 0.07wt% to 0.09wt%, and it might be a solid solution limit of Ln in the present alloy, considering some amount of Ln precipitated as sulfide, phosphide, and oxide. On the other hand, elongation of foil was observed after the oxidation, and it was minimized with the optimum range of Ln content for the oxidation resistance, which suggested that growth stress of the scale was minimized at that range of Ln content.