Microstructure Dependent Fatigue Cracking Resistance of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy

Fatigue cracking behavior from a notch was investigated at room temperature for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloys with four different microstructures obtained at different cooling rates from the β transus temperature. It was found that the alloy with lamellar structures consisting of α/β lamellae or acicular α' martensite laths had a higher fatigue crack initiation threshold from the notch, while the bimodal structure with coarse α grain had a lower fatigue cracking resistance. The alloy with α/β lamellar structure showed a higher fatigue crack growth resistance. The length scales of the microstructures were characterized to correlate with fatigue cracking behavior. Fatigue cracking mechanism related to microstructures was discussed.