Oxidation behavior of the single-crystal Ni-base superalloy DD32 in air at 900, 1000, and 1100°C

The isothermal-oxidation behavior of the single-crystal Ni-base superalloy DD32 was studied over the temperature range from 900-1100 degrees C and analyzed by OM, TGA, XRD, EDX, SED, and EPMA. The alloy DD32 obeyed a subparabolic rate law during oxidation at 900 and 1000 degrees C, while the alloy showed a rather high oxidation rate at 1100 degrees C. The severe composition segregation, which resulted from the solidification process, led to the formation of different scale on the dendritic and interdendritic regions. Internal nitride (AlN) was observed in the subsurface zone of dendritic areas, but absent in interdendritic areas. The oxidation mechanism of the alloy DD32 is discussed by comparing with other alloys.