The isothermal oxidation behaviors of as-deposited and heat-treated Ni–11.5Cr–4.5Co–0.5Al sheet by EB-PVD at 800°C

The isothermal oxidation behaviors for the as-deposited and heat-treated Ni–11.5Cr–4.5Co–0.5Al sheet by EB-PVD were investigated. The annealed of sheet was carried out at 800°C for 16h in 5×10−3Pa. The oxidation exposures were conducted on electrical resistance furnace in 1atm of laboratory air at 800°C up to 120h. The mass gain during subsequent oxidation was measured using a microbalance with a resolution of 10−5g. Surfaces and cross-sections of the oxidized specimens were studied by scanning electron microscopy (SEM). Phase identification of the oxide scale was performed by glancing angle X-ray diffraction (GAXRD) and Energy Dispersive Analysis of X-rays (EDAX). The results show the heat-treated sheet with identical composition exhibited much more stable oxidation behavior than the as-deposited sheet. At 800°C after 96h isothermal exposure, the oxide scales of as-deposited sheet consisted mainly of an external NiO layer, a middle NiO and NiCr2O4 mixed layer and internal rich-Cr2O3 contained cobalt oxide layer. But those of heat-treated sheet exhibits NiO and Cr2O3 mixed layer with <1μm thickness.