The effect of long term exposure in oxidising and corroding environments on the tensile properties of two gamma-TiAl alloys

Scale composition and oxidation mechanism of the Ti–46Al–8Nb alloy in air at 700 and 800 °C

“…It has been reported namely, that during the first stages of oxidation of titanium aluminides, lower titanium oxides, such as Ti 2 O, TiO or Ti 2 O 3 can be formed, which next transform into TiO 2 [29]. One of the transient oxides, Ti 2 O 3, is known to have a corundum structure (rhombohedral) [46], and this could explain the favour- It should not be neglected either that an addition of 8e10% Nb to titanium aluminide alloys remarkably affects their oxidation resistance by limiting the growth of rutile crystals on the surface [52]. This can be associated with the effect of ternary addition on lattice parameters (e.g.…”

Oxidation-induced embrittlement of TiAl alloys

“…Since embrittlement is common to all TiAl-based alloys ( [1][2][3][4][5][6][7][8]) it is clear that, on the basis of the above interpretation, there is no simple way of avoiding embrittlement by changing the composition, although an increase of fracture toughness will reduce the effect of the embrittlement. If the mechanism put forward here is correct the only way to reduce the embrittlement would be the prevention of significant diffusion of oxygen into the alloy.…”

“…However several studies have shown that there is a dramatic loss in mechanical properties, especially room temperature ductility even after a short time exposure at 700 C [1][2][3][4][5][6][7][8]. In several of these papers it was shown that machining off the surface of exposed samples restored the ductility, showing that the problem is surface related.…”

Influence of an oxidation protective coating upon hot corrosion and mechanical behaviour of Ti–48Al–2Cr–2Nb alloy

“…(8e11)) by releasing H 2 gas which attacks preferentially the a 2 -phase present at the grain boundaries leading to an intergranular corrosion. This mechanism implies a self-propagating corrosion process that explains why the corrosion phenomenon is more extensive as the NaCl salt content is increased [28]. In this case, the presence of halogen gases is not beneficial contrary to the so-called "halogen microalloying effect" described by [29] and based on the selective transport of aluminium by gaseous halogen gas from the substrate metal to the oxide scale through pores and micro cracks.…”