Oxidation of Iron-Nickel Alloys

The oxidation of Fe‐Ni alloys in the 500°–1100°C range has been the subject of many investigations. These observations are summarized, and an attempt is made to generalize on the kinetics and mechanism of oxidation. The composition of the oxide film over the entire composition range can be explained in terms of the thermodynamic stability of the oxides of Fe, of , and of .In alloys of all compositions that have been investigated the first reaction is one of selective oxidation, creating a Ni‐rich metal layer at the alloy‐oxide interface. The growth of a Ni‐containing spinel is promoted and formation of is suppressed. This explains the reduction of oxidation rate to about 1000 times less than that of pure iron. The short‐time kinetics of oxidation appears to be governed by diffusion through this Ni‐rich metal layer or by diffusion through the Ni‐containing spinel. Only at the Ni‐rich end of the Fe‐Ni system is observed, and this exists next to the alloy interface under a layer of spinel. The reaction between and is rapid at these temperatures, thus explaining why these two oxides are not observed together. On prolonged reaction, subscale oxidation and intergranular attack is observed. Because of the stratification of oxide layers and these secondary effects, the development of a general rate law would be difficult.