Surface damage of a TiAl-based alloy during high temperature annealing

The near surface stability of a Ti–45Al–2Mn–2Nb alloy has been investigated. Samples of the alloy were annealed at two different temperatures, 1200 and 1000°C for various periods of time. It was found by detailed SEM and TEM investigation that a significant loss of aluminum occurred from the surface of the specimens during annealing, resulting in the formation of Al-depleted damaged layer near the surface of the specimens. The microstructure of the damaged layer was found to be considerably different from that of the bulk. The damaged layer was found to consist of α2 phase near the interface between the damaged layer and the undamaged bulk, and α2 phase and B2 phase with ω-type phase precipitates near the outer edge of the specimen. It was also observed that the thickness of the damaged layer increased with the annealing time and also with the annealing temperature. The thickness of the damaged layer exhibited a parabolic relationship with annealing time for both the temperatures.