Low-cycle fatigue properties of β-type Ti-Mo-Fe alloys with different deformation modes

The low cycle fatigue properties of Ti-10Mo-xFe (x=1,2,3, mass fraction/%) alloys with different plastic deformation modes were studied by OM, SEM, EBSD and electro-hydraulic servo fatigue testing machine. The effects of total strain amplitude (Delta epsilon(t)/2=0.5%, 1.0% and 1.5%) and Fe content on the mechanical response, microstructure and fatigue crack growth behavior of the alloys were analyzed. The results show that the low cycle fatigue properties of the alloys decrease with the increase of strain amplitude and Fe content. The cyclic stress response behavior of each alloy generally shows initial cyclic hardening, followed by cyclic stability or slight cyclic softening until fracture failure. The plastic deformation of Ti-10Mo-1Fe alloy is dominated by {332}< 113 > twinning. With the increase of Fe content, the plastic deformation mode of the alloy changes to dislocation slip. Under low strain amplitude, the number of twins in the fatigue source zone of Ti-10Mo-1Fe alloy is small, and the number of twins along the crack growth direction gradually increases; under high strain amplitude, a large number of twins appear in the near fracture area. The large amount of twins generated and exchanged in the Ti-10Mo-1Fe alloy divides the interior of the grains into a mesh structure, thereby refining the grains, effectively releasing stress concentration and delaying the initiation of fatigue cracks. At the same time, crack deflection occurs when microcracks extend to the vicinity of the twin boundaries, and the large amount of twin boundaries in the alloy effectively prolongs the fatigue crack propagation path.