Co- Effect of Two Kinds of Special Grain Boundaries on High Temperature Oxidation Behavior of Inconel 617 Alloy

The effect of microstructure with high fraction of Sigma 3(n) boundaries and serrated grain boundaries on high temperature oxidation resistance of Inconel 617 is studied. After deformation then slowing cooling treatment, the fraction of Sigma 3(n) boundaries can be increased to over 70%, with simultaneously changing part of the rest random grain boundaries (RGBs) into serrated grain boundaries with the average amplitude of 0.83 mu m and the average wavelength of 15.98 mu m. The formation of serrated grain boundaries is associated with the precipitation of Mo6C and Cr23C6 carbides at RGBs. The microstructure with two types of special grain boundaries (GBs) can effectively improve the high temperature oxidation resistance, which is reflected with significant reductions in the thickness of surface Cr2O3 oxide layer and the formation depth of Al2O3 along the GB. This is attributed to that Sigma 3(n) boundaries, serrated grain boundaries and unconnected straight RGBs network can effectively retard the diffusion of Cr and O elements along the GB.