The Ni-22%Cr-12%Co-9%Mo-1%Al commercial alloy (Inconel 617) was oxidized in air at 1073 and 1173 K under tensile stresses to examine the effect of stressing on its high temperature oxidation. It was shown that the intergranular oxidation was significantly enhanced under the applied stress. The penetration depth increased with creep strain and oxidation time. A maximum depth of 200 μm was observed at 1173 K and at a creep strain of about 5% in 0.5Ms. In stress-free exposure tests the penetration depth was less than 10 μm. The enhanced intergranular oxidation was attributed to the localized fracture of external oxide layers and internal oxides of Al due to grain boundary sliding.
Abrasion of the specimen surface by a 100 grit SiC paper reduced the acceleration of the intergranular oxidation. The abrasion deformed surface recrystallized at the oxidation temperature and formed a fine-grained layer. The displacement at the individual grain boundary in this fine-grained layer was so small that the step height at the surface was decreased. This is believed to be the main cause of reduced intergranular oxidation at the abraded surface.