High temperature oxidation behavior of Ni-based superalloy GH202

The isothermal oxidation kinetic and oxidation behavior of Ni-based superalloy GH202 were investigated at temperatures from 800 degrees C to 1100 degrees C. The microstructure of GH202 was characterized by scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD). The composition and morphologies of oxide scales of the surface and cross-section samples were examined by X-ray diffraction (XRD), electron probe micro-analysis (EPMA), and SEM combined with energy-dispersive spectroscopy (EDS). The results show that the growth of the oxide scales on GH202 obeyed a parabolic law with an activation energy of 247.8 KJ. mol(-1) from 800 degrees C to 1100 degrees C. The continuous and dense oxide scales that formed at 800 degrees C and 900 degrees C were composed of Cr2O3, NiCr2O4 and a small amount of TiO2. Beneath the oxide scales, aluminum-rich oxides formed along the grain boundaries due to internal oxidation. After treatment at 1000 degrees C for 150 h, the oxide scale was separated into two layers, the outer layer with sparse holes that was mainly composed of Cr2O3 and TiO2 and an inner layer of dense Cr2O3. At 1100 degrees C for 100 h the outer layer was spalled, due to the looser oxide scale with large blocks of TiO2 and NiCr2O4 which provided channels for oxygen diffusion. (C) 2016 Elsevier Inc. All rights reserved.