A. Wisbey, K. Lucas, QinetiQ Ltd, Farnborough, United Kingdom

Summary:

The gamma titanium aluminides offer enormous potential for use in aero-engines and other aerospace systems because of the low density and excellent high temperature mechanical properties. They have the potential to replace the heavier nickel alloys for a number of applications, like compressor blades and low pressure turbine blades. However, a significant reduction in the room temperature tensile (especially the ductility) and fatigue properties has been noted following exposure to the expected service conditions of 700°C. Under fatigue conditions a strain range of 0.3% is sufficient to cause very poor fatigue performance after thermal exposure at 700°C. Even temperatures down to 600°C or very short exposures have been found to cause the property reduction. The effects can be so large as to preclude the use of these materials in safety or reliability critical components. In the present work the effect of thermal exposure on the fatigue performance is assessed and more detailed surface analysis has been undertaken in an attempt to determine the cause of this effect, with a view to obtaining a method of mitigating the problem and permit the use of these materials in aerospace systems.