Elevated temperature fatigue crack growth and time dependent behaviour in Ti-6246

Fatigue crack propagation behaviour of the titanium alloy Ti-6246 has been investigated at room and elevated temperatures. Using stress intensity range, DeltaK, as a correlating parameter, fatigue crack growth rates were found to be insensitive to variations in positive mean stress and waveform at 20 degreesC. This is attributed, in part, to the refined microstructure. However, a fine grain size is often associated with inferior high temperature creep behaviour and can accentuate the diffusion of aggressive species along grain boundaries. As a result, at the higher temperatures measured growth rates generally increased and became dependent on R ratio and periods of dwell loading at peak stress. Additional testing under a hard vacuum condition have been implemented to characterise creep-environmental fatigue interactions.