Affects of applied stresses on the isothermal and cyclic high-temperature oxidation behavior of superalloys

In this investigation, the affect of applied tensile stresses on the isothermal and cyclic oxidation behavior of nickel-based superalloys was studied. The influence of applied stresses was investigated through measurements of specific mass change, oxide morphology and thickness, degree and depth of internal oxidation, and compositional changes in and around the oxide scales. It was determined that an applied tensile stress generally led to larger Cr/Ni ratios in the oxide scales, greater overall chromium depletion values directly under the oxide scales, lower specific mass change values, and thinner oxide scales. These affects are attributed to a greater concentration of dislocations, defects, etc. in the materials caused by the applied stress. These defects act as fast diffusion paths for the Cr atoms to diffuse to the surface, and thus, cause a reduction in the duration of the less protective transient oxidation period, and promote a faster formation of the protective Cr2O3 layer.