On High Temperature Oxidation of Chromium: I . Oxidation of Annealed, Thermally Etched Chromium at 800°–1100°C

Oxidation of annealed, thermally‐etched chromium has been studied at different oxygen pressures ranging from in the temperature range 800°–1100°C. A varied oxidation behavior is observed: at and 800°C the oxidation is approximately logarithmic, while above 900°C it is parabolic followed by repeated breakdowns and protective stages. At reduced oxygen pressures the oxidation behavior changes and becomes linear at the lower oxygen pressures. The different kinetics are correlated with properties of the scales which may crack, wrinkle, or balloon depending upon the reaction conditions. Large compressive stresses are built up in the scales during oxidation and the ability of the scale to deform increases dramatically with decreasing partial pressure of oxygen. Under most conditions the oxide scales become detached from the metal substrate. It is concluded that volume diffusion and transport along cracks and grain boundaries contribute to the growth of scales.