The Role of Oxygen Partial Pressure on the Nature of the Oxide Scale on a NiCr Model Alloy
Résumé
The high-temperature oxidation behavior of a binary Ni-30Cr model alloy has been studied at 1050 °C at three oxygen partial pressures p(O2): ~10−14, ~10−10, and ~10−5 atm. The oxide scales were characterized using grazing X-Ray diffraction, Raman spectroscopy, EDX spectroscopy, and TEM microscopy. The semiconducting properties of the oxide scale have been investigated using photoelectrochemistry (PEC). Classical characterizations show that chromia is the main oxidation product whatever maybe the oxygen activity. PEC reveals additionally the presence of (i) n-type Cr2O3 at p(O2) ~ 10−14 atm and (ii) both n-type and p-type Cr2O3 at higher oxygen pressures. The mechanisms of oxidation are discussed as a function of the major point defects that govern the oxide scale growth.