The oxidation behavior of Ti–46.5Al–5Nb at 900 °C

The early stages of Ti–46.5Al–5Nb (at%) oxidation at 900 °C have been investigated combined with TEM and STEM. The results reveal that a layer composed of polycrystalline TiO2 and amorphous Al2O3 phase formed firstly after 5-min oxidation. The base alloy connected with the oxide scale has some deformation compared with the inner full lamellar TiAl structure. After 30-min oxidation, the phases of γ-Al2O3, κ-Al2O3, titanium nitrides and Ti5Al3O2 were formed in the area from the nitride layer to base alloy. After 50 h of oxidation, Ti5Al3O2 vanishes at the interface of oxide scale/base alloy in Ti–46.5Al–5Nb, contrary to the continuous formation of Ti5Al3O2 in γ-TiAl at the interface of oxide scale/base alloy, Al3Nb phase formed in this zone, which hinders the continuous formation of Ti5Al3O2.