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

摘要

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 degrees C and 1100 degrees 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, NiCr2O4 and other complex compounds and spinel phases, an inner continuous layer of alpha-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 degrees C, the Al2O3 film formed in the initial time is unstable, discontinuous and incompact and the inner Al2O3 layer formed after 300 h oxidation is porous. (C) 2017 Elsevier B.V. All rights reserved.