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

Abstract

The low-cycle fatigue （LCF） behavior of Ti-10Mo-xFe （x=1， 2， 3，mass fraction/%） alloys with different plastic deformation modes were investigated by OM， SEM， EBSD and electro-hydraulic fatigue test machine. The effects of the strain amplitudes （Δεt/2=0.5%， 1.0% and 1.5%） and Fe content on the mechanical response， microstructures and fatigue crack propagation behavior were analyzed. The results show that the low-cycle fatigue performance of the alloys decreases with the increase of strain amplitude and Fe content. The cyclic stress response behaviors generally exhibit an initial cyclic hardening and then tend towards a cyclic stability or slight cyclic softening until fracture. The plastic deformation mode of Ti-10Mo-1Fe alloy is dominated by ｛332｝〈113〉 twinning， and changes to dislocation slip with the increase of Fe content. A few twins are formed in the fatigue initiation region of Ti-10Mo-1Fe alloy under low strain amplitude， and the twin area fraction increases gradually along the crack propagation direction， while a large number of twins are activated near the fracture area under high strain amplitude. The activation and intersection of abundant twins in Ti-10Mo-1Fe alloy divide the grain into network microstructures， which effectively release the stress concentration and delay the initiation of fatigue crack due to the dynamic microstructure refinement effect. At the same time， the abundant twin boundaries significantly extend the fatigue crack propagation path because the micro-crack deflects along the twin boundaries.

Keywords

• β-type titanium alloy
• low-cycle fatigue
• twinning-induced plasticity affect
• ｛332｝〈113〉 twin
• dislocation slip