Correlative atom-probe tomography and transmission electron microscope study of a chemical transition in a spinel on an oxidized nickel-based superalloy

Complex thermally grown oxides (TGOs) are formed on a single-crystal Ni-based superalloy due to a large fraction of alloying elements. Combining atom-probe tomography and transmission electron microscopy analyses, the three-dimensional elemental distributions of metal oxides of the spinel and refractory metal-oxide regions are presented. A spinel-type oxide, Ni(Cr,Al)(2)O-4, is formed with a crystallographic orientation relationship with the alloy substrate, which decomposes into other oxides. The sequence of oxides observed in the TGO are NiO -> Cr2O3 -> Ta2O5 -> NiTaO4, NiTa2O6 -> Ni(Cr,Al)(2)O-4 -> Al2O3. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.