Low-cycle fatigue behavior and property of TA15 titanium alloy with tri-modal microstructure

Low-cycle fatigue (LCF) behavior and property characteristics of titanium alloy with a tri-modal microstructure, consisted of equiaxed alpha (alpha(p)), lamellar alpha (alpha(1)) and beta transformed matrix (beta(t)) were explored in this work. The results show that, at different strain amplitude (epsilon(ta)) levels, the cyclic hardening/softening is determined by the competition (epsilon(ta) < 0.9%) or superposition (epsilon(ta) >= 0.9%) effect of the variations of back stress and friction stress. As well, the fractography shows remarkably different features at different epsilon(ta) levels. When epsilon(ta) ation region indicates a faster crack propagation. The above divisional LCF behavior and fracture features determine a twopart linear Coffin-Manson relationship. On the other hand, increasing a content could delay the fatigue crack nucleation and propagation due to its positive effect for improving deformation compatibility. This will effectively increase the LCF life. However, increasing alpha 1 content would produce al colonies, which promote the dislocation slip and reduce the slip reversibility. So, the crack nucleation and propagation will be facilitated and then the LCF life is decreased.