Micro-scale mechanism for cyclic deformation behavior in Zirconium under low-cycle-fatigue loading

Abstract

Cyclic deformation behaviors and damage mechanisms of pure Zr were systemically investigated at fully reversed strain-controlled tension-compression fatigue experiments (R = −1), followed by detailed microstructural characterization using scanning electron microscopy with electron backscatter diffraction and transmission electron microscopy. The results demonstrated that three stages (Ⅰ, Ⅱ, Ⅲ) of cyclic response behavior were observed for all applied strain amplitudes, and the trend of the cyclic stress response mainly originated from the substructure evolutions. The initial cyclic softening was attributed to the formation of alternating high- and low-dislocation-density regions, enhancing the free path of dislocation motion. The fatigue life prediction model was established based on the hysteresis loops strain energy. SEM/EBSD slip traces analysis and TEM double beam diffraction analysis showed that prismatic <a> dislocation slip was the dominating deformation mechanism, and pyramidal <c + a> dislocations and 101¯2 twins played an essential role in accommodating plastic deformations. Further, fatigue damage behavior was not only influenced by initial texture, but also other factors played an essential role.