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.

Research highlights
► Serrations in the plastic deformation regions of hysteresis loops increase with increasing strain amplitude.
► The appearance of DSA depends on the optimum combination of temperature, strain amplitude and strain rate.
► The stress humps appearing at the stress curves result from the formation of strain-induced micro twins.