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

摘要

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 deg C for 16 h in 5 X 10~(-3) Pa. The oxidation exposures were conducted on electrical resistance furnace in 1 atm of laboratory air at 800 deg C up to 120 h. The mass gain during subsequent oxidation was measured using a microbalance with a resolution of 10~(-5) g. 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 deg C after 96 h isothermal exposure, the oxide scales of as-deposited sheet consisted mainly of an external NiO layer, a middle NiO and NiCr_2O_4 mixed layer and internal rich-Cr_2O_3 contained cobalt oxide layer. But those of heat-treated sheet exhibits NiO and Cr_2O_3 mixed layer with < 1 mu m thickness.