Influence of temperature on passive film properties on Ni–Cr–Mo Alloy C-2000

• The passive films on Alloy C-2000 were investigated by AR-XPS and ToF-SIMS.
• The film consists of an inner Cr2O3, outer Cr/Ni hydroxide and Mo/Cu oxides.
• Increasing temperature leads to thickening of both layers which improves passivity.
• Increasing temperature leads to loss of Cr2O3 from inner, Mo/Cu from outer layers.
• These compensating effects make passive current almost independent of temperature.

The properties of the passive film on a Ni–Cr–Mo alloy, Alloy C-2000 (Ni–23Cr–16Mo–1.6Cu), grown at various temperatures, were investigated by AR-XPS and ToF-SIMS. The presence of a layered structure in the passive film has been demonstrated at low and mild temperatures in neutral solutions, with an inner Cr2O3 layer, outer Cr/Ni hydroxides layer and Mo/Cu oxide in the outermost surface. As temperature increases, the thickness of both layers increase which improves passivity. Increasing temperature leads to a loss of Cr2O3 from the inner and of Mo/Cu from outer layers. These compensating effects make the passive current density almost independent of temperature.