Thermodynamic investigation of oxidation behavior of NiAl intermetallics with embedded Cr and MoFriday (21.08.2020) 08:20 - 08:20 Poster Room Part of:
The isothermal oxidation of NiAl alloys with embedded Cr bar was studied in a thermobalance at 800 °C, 1200 °C and 1300 °C for 50 hours under Ar atmosphere containing 13 vol.% O2. An almost pure Cr2O3 layer was formed over Cr. A thin α-Al2O3 scale was formed on the NiAl matrix at a sufficient distance from the interface of NiAl and the Cr bar. The formation of a continuous Al2O3-Cr2O3 solid solution was observed in the vicinity of the interface of NiAl and Cr at high temperatures. The composition of the solid solution changed from almost pure Al2O3 near the metal matrix to almost pure Cr2O3 near the gas surface.
The oxidation behavior of the directionally solidified NiAl-34Cr was also investigated similar to the coarse NiAl-Cr composite at 1200 °C and 1300 °C. More spallation of the oxide scales was seen during oxidation of DS NiAl-34Cr compared to the coarse NiAl-Cr composite.
A similar procedure was performed for NiAl with embedded molybdenum wire at 800 °C. A rapid weight loss was observed during oxidation in the thermobalance which was due to formation of volatile Mo oxides. Most of the formed oxides evaporated which made further investigation of the interface of NiAl and Mo impossible.
A thermodynamic database for Ni, Al, Cr, Mo and O, which includes data for pure elements and their corresponding binaries and ternaries, was established and used to predict the stability range of different phases during oxidation