Surface preparation effect on oxidation kinetics of Ni-base superalloy

In the present study an oxidation behavior of commercially available Ni-base superalloy IN 713C with different surface finishing, namely polished up to 1 mu m diamond paste (resulting in R-a=0.023) and ground by SiC paper with 80 grit (R-a=1.23), were investigated at 950 degrees C in air. It was found that ground sample developed very thin, protective alpha-Al2O3 scale. Moreover, locally formation of theta-Al2O3 in the forms of spikes was observed. For the sample with polished surface formation of outer chromia scale accompanied with internal oxidation of aluminum was observed. Moreover, for specimen which does not form continuous alumina scale or sub-scale, the GD-OES depth profiles showed an enrichment of boron at the oxide scale/alloy interface. It was proposed that the formation of protective alumina scale on ground samples is caused by introducing the defects into the near-surface region of the material, which are an easy diffusion paths for the elements forming a protective oxide scales.