Abstract
The isothermal oxidation behavior of Ni-15Cr sintered alloys with 1.0 mass% of dispersion of various rare earth oxides was studied in air at 1473 and 1523 K. The oxidation rate was very dependent on the type of the dispersoid. The dispersion of rare earth oxides except for Eu2O3 reduced the oxidation rate at 1473 K; whereas, the dispersion of Eu2O3, Dy2O3, Ho2O3, Yb2O3 and Lu2O3 increased the oxidation rate at 1523 K. The spalling of the scale was also dependent on the type of the dispersoid. All the rare earth oxides suppressed the spalling of the scale at 1473 K, while the rare earth oxides other than La2O3, Gd2O3, Tb2O3 and Er2O3 lost their effect on the suppression in the spalling of the scale at 1523 K. The dispersion of La2O3 showed an excellent effect both on the reduction in the oxidation rate and spalling of the scale.
NiO content increased in the scale formed on the alloys which showed large mass gain; whereas a single layered Cr2O3 scale without NiO was maintained on the alloys which showed better oxidation resistance. These results suggested that the rare earth oxides which induced into the scale might change the diffusivity and/or solubility of Ni ions in the Cr2O3 scale.
