Interfaces in Oxides Formed on NiAlCr Doped with Y, Hf, Ti, and B

This study applies atom probe tomography (APT) to analyze the oxide scales formed on model NiAlCr
alloys doped with Hf, Y, Ti, and B. Due to its ability to measure small amounts of alloying elements in the oxide
matrix and its ability to quantify segregation, the technique offers a possibility for detailed studies of the dopant’s
fate during high-temperature oxidation. Three model NiAlCr alloys with different additions of Hf, Y, Ti, and B
were prepared and oxidized in O2 at 1,100°C for 100 h. All specimens showed an outer region consisting of
different spinel oxides with relatively small grains and the protective Al2O3-oxide layer below. APT analyses
focused mainly on this protective oxide layer. In all the investigated samples segregation of both Hf and Y to the
oxide grain boundaries was observed and quantified. Neither B nor Ti were observed in the alumina grains or at
the analyzed interfaces. The processes of formation of oxide scales and segregation of the alloying elements are
discussed. The experimental challenges of the oxide analyses by APT are also addressed.