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.