The oxidation of five Ni-Fe alloys with Ni of 5-50% has been studied in air at 8001 300°C for 15120 min. The scales consisted of the external scale and the subscale.
The external scales had stratified structures of either α-Fe₂O₃/Fe₃O₄ or α-Fe₂O₃/Fe₃O₄/(FeO+Fe₃O₄), depending on the conditions such as the nickel contents in the alloy, the oxidation temperature and the time of exposure. Their thicknesses decreased with increasing nickel contents in the alloys. FeO grew with a characteristic shape in the scales of the 530% Ni alloys oxidized at 1 0001 200°C.
The subscales consisted of the metal/oxide mixed zone and the intergranular attacked zone. Morphological studies showed that the subscale was formed by the very local oxidation at the grain boundaries and at the alloy/mixed zone interface. Both zones grew according to the parabolic rate law. The effect of nickel contents in the alloy on the subscale growth rate was studied.
On the basis of the above results, the aspects of the oxidation of Fe-Ni alloys were discussed.