The behaviour of 800H nickel (Ni)-based alloy under isothermal oxidation condition was study in this paper. The isothermal oxidation behaviour was examined in terms of fine grained and coarse grained 800H Ni-based alloy obtained from heat treatment operation at 1000 °C and 1150 °C, respectively. The heat-treated samples were undergo an isothermal oxidation attempt at 500 °C in laboratory air for 500 hours exposure duration. The effects on the oxidation kinetics was examined in terms of weight change measurement. In addition, the effects on the oxide scale growth was observed in terms of phase analysis using XRD technique and surface morphology analysis using FESEM outfitted with EDX spectrometer. As a results, both fine grained and coarse grained 800H Ni-based alloy were obey a parabolic rate law showing that the oxide growth rate was followed a diffusion-controlled mechanism. Additionally, fine grained 800H Ni-based alloy sample exhibited a inferior oxidation rate compared to coarse grained sample. The XRD analysis exhibited that the oxides scale composed of Cr2O3, TiO2 and MnCr2O4. The observation on the oxide scale morphology indicate that uniform oxide scales were formed on the alloy surface of both samples. However, coarse grained 800H Ni-based alloy recorded an oxide exfoliation which indicate poor oxidation protection.
