Oxidation mechanism of Ni-20Cr thin strips and effect of a mechanical loading

The oxidation behaviour of Ni-20Cr foils of 200 mu m thickness was studied in air at 600 degrees C and 900 degrees C. The oxide morphology and nature were determined by SEM and TEM. The scales formed at all temperatures were complex, with an outer NiO layer and an intermediate layer of equiaxed NiO, NiCr2O4 and Cr2O3 grains. At 600 degrees C, internal oxidation of chromium occurred in the substrate while a continuous Cr2O3 layer was observed at 9 00 degrees C. The effect of a tensile load on the oxidation kinetics and me chanism of Ni-20Cr alloy was also examined. The results indicated that appl ying a tensile load did not modify the oxide nature and morphology but indu ced an increase of the oxidation rate, promoting the formation of internal oxidation at 600 degrees C, and of a NiCr2O4 layer at 900 degrees C.