Research on high-temperature oxidation resistance behavior of TNM titanium aluminum alloy

TNM(Ti–43Al–4Nb–1Mo–0.1B) titanium aluminum alloy has low density, excellent mechanical properties at high temperatures, and good deformation ability at high temperatures and is applied as a new-generation aeroengine low-pressure turbine blade material. Its long-term service temperature can reach approximately 750 ℃. In this paper, a TiAl alloy with a nominal composition of Ti–43Al–4Nb–1Mo–0.1B (atom fraction, %) was prepared using the vacuum induction levitation melting method. Oxygenation samples with dimensions of 10 mm×10 mm×5 mm were fabricated using electrical discharge wire cutting. After sandpaper polishing, the surface of the samples was selected for oxidation testing in air at two different temperatures of 700 ℃ and 760 ℃ for nine oxidation time points of 1–200 h using a muffle furnace. A systematic investigation was performed on the oxidation behavior of the TNM alloy at different temperatures and time exposures by characterizing its surface morphology and surface and cross-sectional oxide composition using scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. Results revealed that at 700 ℃ and 760 ℃, the TNM alloy displays complete oxidation resistance and antioxidation levels and the weight gain rate of the sample at 760 ℃ is 0.1956 g·m⁻²·h⁻¹, which is much higher than that at 700 ℃. At 700 ℃, the TNM alloy initially forms TiO₂ during the early stage of oxidation, followed by a gradual increase in Al₂O₃ until it covers the entire sample. After 200 h of oxidation, the predominant surface oxides on the alloy were Al₂O₃ with small amounts of MoO₂ and MoO₃, which exhibited excellent oxidation resistance. At 760 ℃, the alloy forms unstable oxide compounds of Al and Ti during the initial stage of oxidation, and the growth rate of TiO₂ is faster, destroying the continuous and dense Al₂O₃ layer on the surface and making the matrix more easily oxidized. After 200 h of oxidation, the predominant oxide on the surface is mainly TiO₂ with small amounts of MoO₂, MoO₃, and other molybdenum oxides, with the oxidized surface of the TNM alloy exhibiting a typical multilayer structure of a TiO₂ layer (outermost layer) + an Al₂O₃ layer + a mixed layer (consisting of Ti, O, Nb, Mo) + substrate. Furthermore, the thickness of the oxide layer is significantly greater at 760 ℃ than at 700 ℃.