The effect of high temperature exposure on the tensile properties of g TiAl alloys

The lightweight *g titanium aluminide alloys offer good mechanical properties for gas turbine applications at temperatures up to 700 deg C. An important characteristic of these materials will be their mechanical performance after exposure to anticipated service temperatures. Thus cast Ti-46Al-2W and extruded Ti-46A1-5Nb-1 W have been subjected to thermal exposure at temperatures between 500 and 700 deg C for up to 1000 h. 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 room temperature tensile strength and ductility reduced significantly. The room temperature property reductions were thought to be associated with changes in the surface residual stress state. Other potential factors include premature surface cracking, due to either localised hydrogen or oxygen embrittlement.