The kinetics of oxide film growth on Maraging steel as described by space‐charge effects

The oxidation kinetics of a grade 300 maraging steel in air at temperatures ranging from 300 to 600 °C have been determined using Auger electron spectroscopy in conjunction with argon ion sputtering. A limited‐thickness type of growth was observed up to the relatively high temperature of 480 °C. Above 480 °C, the kinetics were parabolic. A thin gold layer sputtered onto the surface before oxidation resulted to a change in the kinetics from limited‐thickness to approximately parabolic growth at temperatures below 480 °C, while it remained parabolic above 480°C. The limited‐thickness oxide growth is described in terms of space‐charge effects, as outlined by the theory of Formhold. The insulating properties of a thin mixed spinel oxide present at the metaloxide interface is critical in bringing about the space charge in the oxide. A change in the electrical conductivity of the mixed spinel is associated with a change in the oxidation kinetics.