Dynamic strain aging in low cycle fatigue of duplex titanium alloys

The influence of dynamic strain aging (DSA) on low cycle fatigue (LCF) in duplex Ti-6-4 and SP700 titanium alloys was studied. LCF was performed within the temperature range from 350 °C to 450 °C, at strain rates of 10−3 s−1 and 10−4 s−1, and strain amplitudes of 1.25% and 2%. DSA appeared as serrations at the plastic portion of the cyclic stress–strain hysteresis loop, as well as stress humps appearing in the cyclic stress response (CSR) curve of peak tensile stress response versus cycle number. Strain-induced micro twin formation was only observed in the sample after fatigue with 2% strain amplitude under a 10−4 s−1 strain rate, indicating that it is a DSA induced phenomenon.