The lightweight y titanium aluminide alloys offer good mechanical properties at temperatures up to 700°C for gas turbine applications. An important characteristic of these materials will be their mechanical performance after exposure to anticipated service temperatures. Thus cast Ti-47Al-2W and extruded Ti-46Al-5Nb-lW have been subjected to thermal exposure at temperatures between 500°C and 700°C for up to 1000 hours. This showed that the bulk microstructure was stable and resulted in little or no change in tensile properties after exposure. However, once surface effects were included in the tensile properties, then the values of both tensile strength and ductility reduced significantly. This is thought to be associated with cracking at the surface, due to either the thin (～1 μm thick) oxide formed at elevated temperatures or, more likely, along favourably oriented and embrittled α{sub}2 laths. However, other factors also probably contribute to the reduced tensile performance.
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