Oxidation of Ni-base alloys in atmospheres with widely varying oxygen partial pressures

The oxidation behavior of the Ni-base alloys IN 617, IN 713 LC, Ni20Cr, and Ni20Cr+Si has been investigated in the temperature range from 850°C to 1000°C in air and at low-oxygen partial pressure p(O2) (10−19 to 10−16 bar). With the exception of alloy IN 713 LC, the materials show no influence of p(O2) on the oxidation mechanisms and the kinetics. This result can be explained by the formation of a dense Cr2O3 layer, the growth rate of which is controlled by the Cr ion interstitial concentration in Cr2O3 at the phase boundary oxide/alloy and the mobility of Cr ions in Cr2O3. For the alloy IN 713 LC which develops a dense Al2O3 layer in air, a modified transition mechanism at low p(O2) leads to the formation of Cr2O3 at the surface and a strong internal oxidation of Al.