High Cycle Fatigue and Range-Mean Performance of Emerging Titanium Alloys for Aeroengine Applications

Four alpha-beta titanium alloys, containing increased beta stabilising elements when compared to the well established Ti-6Al-4V, were previously characterised for their low cycle fatigue behaviour and resistance to cold dwell sensitivity. The same four alloys are now assessed for high cycle fatigue performance, employing plain cylindrical and notched specimen geometries. Fatigue strength under load-controlled cycling was measured under two contrasting mean stress conditions, a fully reversed R = −1 waveform and a positive mean stress waveform of R = 0.3. The role of microstructure and micro-texture are considered to explain the relative high cycle fatigue behaviour of each alloy and in particular the mechanisms responsible for fatigue crack initiation. The data are subsequently employed to construct “safe stress” range-mean diagrams.