Oxidation Behavior of Two‐Phase Alloy Fe‐44 w/o Cu

Abstract

The oxidation of a two‐phase iron‐copper alloy has been studied as an example of the behavior of multiphase systems with simple compositions of the component single phases. The alloy oxidizes more slowly than either of the pure metals, particularly iron, and the scale contains both components, copper being particularly accumulated close to the scale‐gas interface. A deep region of internal oxidation is also present, where the iron‐rich particles have been converted into normalFeO . Possible reasons for the observed reduction of the oxidation rate in comparison with pure iron are examined: by means of an approximate calculation based on the theory of the growth of multilayer scales it is concluded that a major fact is the thermodynamic destabilization of the fast growing wustite phase, due to the low iron activity at the alloy‐scale interface. No particular effect of growth stresses, due to the anticipated differences in oxidation rate of the component phases, has been observed. Instead, in agreement with the observation that the scale composition is rather uniform laterally and shows the largest changes perpendicularly to the alloy surface, the two‐phase nature of the alloy does not seem to exert a strong influence on the overall oxidation behavior.