Oxidation of Ni-Cr alloy at intermediate oxygen pressures. I. Diffusion mechanisms through the oxide layer

• Oxidation of Ni-30Cr has been studied in oxygen atmospheres in Rhines packs.
• The effect of the oxygen pressure on the oxidation behaviour is discussed.
• Transition from interstitial to vacancy mechanism for oxide growth is estimated.
• Permeability and diffusion coefficients of chromium in Cr2O3 layer are determined.

The oxidation behaviour of Ni-30Cr alloy and the kinetics of the sole growth of Cr2O3 have been studied at 1150 °C up to 289 h at oxygen pressures comprised between 10−13 and 10−3 atm, thanks to Rhines pack device. Oxide morphology, growth mechanisms and kinetics are discussed in terms of nature, concentration and diffusion of point defects. The criteria ruling the nature of the major diffusing point defects are considered through the influence of temperature and oxygen pressure. Diffusion coefficients are calculated from the oxidation kinetics data and compared to the literature.