Effect of Oxygen on High-temperature Phase Equilibria in Ternary Ti-Al-Nb Alloys

Alloys based on titanium aluminides received a lot of attention because of their capability to substitute Ni-based superalloys in high-temperature applications. However, the phase equilibria between the main microstructure constituents (αTi), (βTi), γ (TiAl) and α₂ (Ti₃Al) can be shifted significantly by impurities such as oxygen especially at high temperatures. This behavior is investigated on the tie-triangle (αTi) + (βTi) + γ (TiAl) in the ternary Ti-Al-Nb system at 1300 °C. An explanation for this behavior could be the occupation of octahedral voids by impurities in certain phases.