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)2O4, 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)2O4 → Al2O3.