High cycle fatigue behavior of Ti–5Al–5Mo–5V–3Cr–1Zr titanium alloy with lamellar microstructure

High–cycle fatigue (HCF) damage behavior of Ti–5Al–5Mo–5V–3Cr–1Zr (Ti–55531) titanium alloy with lamellar microstructure (LM) was systematically investigated at room temperature. Results indicate that both grain boundary (GB) α phase and small–scale (~10 µm) heterogeneous microstructure regions (SHMRs) in prior β grains are weak microstructures in LM. Microcracks nucleate at prior β GBs caused by fracturing of some GB α during HCF loading. Dislocations nucleate and annihilate at α/β interfaces, which promote strain concentration and microcracks initiation at α/β interfaces in SHMRs. A combination of slip and twinning predominate cyclic deformation in α lamellae, which leads to nucleation of microcracks at α lamellae in SHMRs. Small cracks grow along α/β interfaces or transfer across α lamellae, and then form relatively long cracks in β grain interiors. Such crack initiation and propagation behaviors promote the HCF fracture of the alloy.