Oxidation behavior of Fe-Ni-Co based superalloys and influence of yttrium addition

The oxidation behavior of three Fe-Co-Ni based superalloys with different y ttrium additions were investigated at 650 degrees C in air. The oxidation k inetics of the three alloys follows parabolic law initially, then follows l inear law. The oxide scale formed on all three alloys consists mainly of Co dissolved Fe3O4 and partly of FeO and Fe2O3 in which Fe3O4 acts as a prote ctive layer. An yttrium addition into the Fe-Co-Ni based superalloys improv es their oxidation resistance by reducing the micro-defects in the scales. Thus, the weight gains of the alloys during the oxidation are reduced, and the transition of parabolic law to linear law is postponed. Pegging was obs erved on the cross section of alloy with 0.08 wt pet yttrium addition after the oxidation.