Effect of microstructure on notch fatigue properties of Ti-6Al-4V

The effect of microstructure on the notch fatigue properties of Ti-6A1-4V was investigated. Specimens with five distinctly different microstructures were tested and subsequently examined in detail. It was found that the notch fatigue performance of the alloy varied significantly as the microstructure was altered by heat treatment. The best high cycle fatigue strength was found in specimens heat treated above the beta transus temperature, containing an almost totally transformed acicular alpha structure. The fatigue performance of specimens with this microstructure appeared to be controlled by the size of the nucleated crack. It is suggested that at low stress levels the nucleated crack is limited in size to the width of a single alpha needle, while at high stresses the nucleated crack may be as large as an entire colony of similarly aligned alpha needles.