Abstract
The thermal, surface properties and microstructures of the nitrided γ-Ti-46Al–2Nb and Ti–46Al–2Nb-0.7Cr-0.3Si intermetallic alloys were investigated. These vacuum-melted alloys were annealed at 1100 °C to stabilize the (α2+γ) lamellae structure. Moreover, the annealed alloys were further annealed at 900 °C under nitrogen gas (nitridation). The alloys microstructures and nitride surface coatings were characterized. The Ti–46Al–2Nb alloy was comprised of γ-TiAl, α2-Ti3Al and β-phases after the annealing, while the Ti–46Al–2Nb-0.7Cr-0.7Si alloy revealed the Ti5Si3, γ-TiAl and α2-Ti3Al phases. Thin nitride layers formed on both alloys. After cyclic oxidation, the nitrided alloys exhibited surface spallation at different rates. The X-ray photoelectron spectroscopy (XPS) revealed the presence of mixed oxide layer of Al2O3, Cr2O3 and SiO2 near the Ti–46Al–2Nb-0.7Cr-0.7Si surface.
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