Cyclic softening of the Ti-10V-2Fe-3Al titanium alloy

The β-metastable Ti-10V-Fe-3Al alloy is studied in low cycle fatigue (LCF) at room temperature. An acicular and two equiaxed αp structures aged at different temperatures were produced and specimens were tested under plastic strain control. The experimental results show that the Ti-10V-2Fe-3Al alloy softens cyclically. The amplitude of the softening is not affected by the microstructure and it decreases as the applied plastic strain increases. The investigations show that this phenomenon proceeds from a decrease in both the isotropic and the kinematic components of the stress. The deformation modes have been analyzed by transmission electron microscopy (TEM) after the cyclic softening stage. Homogeneous prismatic slip is mainly observed in the α-phase. Furthermore, abundant cross-slip of <a> dislocations and <c+a> slip are also observed. The kinematic decrease is associated with a process of grain-to-grain homogenization of yielding through the microstructure, and the isotropic softening with dislocations annihilation enhanced by cross-slip in the α-phase. Quantitative TEM analysis with regard to the crystallographic orientation of α, particles indicates that the decrease in the softening amplitude at high levels of the applied plastic strain must be related to the occurrence of 〈c+a〉 slip.