Long-term oxidation behavior and mechanism of DD6 Ni-based single crystal superalloy at 1050 °C and 1100 °C in air

By virtue of XRD, OM, SEM and EDS, detailed oxidation behaviors for 2000h exposure of DD6 Ni-based single crystal superalloy ware investigated at 1050 °C and 1100 °C. The oxidation kinetic curves both follow the parabolic law in the first stage, during which time the oxidation behaviors in interdendritic area and dendrite core area are different. With the oxidation time continuing, the morphologies of the oxides in these two kinds of areas gradually tend to coincide: An outer columnar (Ni, Co)O, an intermediate layer mainly composed of NiTa₂O₆, CoCo₂O₄, CoWO₄, NiCr₂O₄and other complex compounds and spinel phases, an inner continuous layer of α-Al₂O₃. The double diffusion of oxygen anions and Ni and Co cations developed inwards and outwards respectively is responsible for the morphology of the oxide scale. At 1100 °C, the Al₂O₃film formed in the initial time is unstable, discontinuous and incompact and the inner Al₂O₃layer formed after 300 h oxidation is porous.