Diffusional Growth of Oxide Scales on Cobalt-Iron Alloys

Abstract

<p>In this thesis the results of an experimental investigation and theoretical analysis of high temperature oxidation properties of cobalt-iron alloys are presented. Cobalt-iron alloys containing up to 70% iron were subjected to pure oxygen atmospheres with pressures ranging from 10ˉ⁴ to 1 atm at 1200°C. The reaction kinetics, oxide scale morphologies and spatial distributions of the reacting species in the oxidized specimens were determined. It has been established that the reaction is controlled by metal diffusion through the oxide scales separating the reactants. A ternary diffusion model was invoked to describe the high temperature oxidation behaviour of the investigated alloys. The consistency of the model is tested by evaluating the concentration profiles from metal diffusion coefficients and nonstoichiometry of ternary oxides using the Wagner phenomenological equations. The comparison of the results from theoretical calculation suggests that the theoretical analysis adapted in this work is consistent with the actual physical and chemical processes governing the oxidation reaction.</p>