Occurrence of dynamic strain aging in Alloy 617M under low cycle fatigue loading

Low cycle fatigue (LCF) behavior of solution annealed Alloy 617M forging is studied at 300, 573, 773 and 973 K using strain amplitudes ±0.25, ±0.4, ±0.6 and ±0.8% at a nominal strain rate of 3 × 10−3 s−1. The alloy evidenced the occurrence of dynamic strain aging (DSA) in the temperature regime 573-973 K caused by solute-dislocation interactions and the extent of interactions have been linked with the frequency and magnitude of stress drops/serrations on the hysteresis loops. The cyclic stress response, the hardening evolution curves, the frequency and magnitude of serrations on the hysteresis loops have been critically assessed in the framework of temperature-strain amplitude combination that affects the underlying fatigue deformation and the damage evolution process. At lower temperature-strain amplitude combination, the locking type B serrations appear from first cycle onwards that is persistent during the entire fatigue life. At 973 K, delayed strains for first serration to appear on hysteresis loop and disappearance of the type C serrations towards the later part of deformation have been associated with in-situ precipitation.