Journal
INTERNATIONAL JOURNAL OF PLASTICITY
Volume 118, Issue -, Pages 105-129Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijplas.2019.02.006
Keywords
Dislocation annihilation mechanisms; Low cycle fatigue; Critical annihilation distance; Fatigue life model; Sanicro 25
Funding
- National Natural Science Foundation of China [51475326]
- Demonstration project of national marine economic innovation [BHSF2017-22]
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Dislocation annihilation behavior of Sanicro 25 alloy was investigated based on various total strain amplitudes (Delta epsilon(t)/2). The slopes of cyclic stress response curves during stage II were compared and showed that obvious stable cyclic behavior occurred at Delta epsilon(t)/2 = 0.3%. Microstructure analysis reveals that the number of slip plane increased with increasing Delta epsilon(t)/2. When Delta epsilon(t)/2 = 0.3%, dislocations can slip on the slip plane (11 (1) over bar). When Delta epsilon(t)/2 increased to 0.4%, the slip planes included ((1) over bar 11) and (11 (1) over bar). The fraction of substructured grains under Delta epsilon(t)/2 = 0.3% was obviously larger than that under (Delta epsilon(t)/2) = 0.4%, which was attributed to the obvious dislocation annihilation. The deformed grains were dominant at Delta epsilon(t)/2 = 0.4%. The annihilation mechanisms of dislocations were analyzed during tensile and compressive loading based on the cyclic stress-time curves. The results showed that when Delta epsilon(t)/2 = 0.3%, during stage II, dislocation annihilation mainly occurred during compressive loading. Dislocation annihilation included annihilation caused by cross-slip of screw dislocations and annihilation of adjacent edge dislocation dipoles. Furthermore, considering the critical annihilation distance between two adjacent edge dislocation dipoles, a modified dislocation annihilation model was presented. The dislocation annihilation model was verified based on the actual annihilation rate of dislocations. Further, the relationship of microstructure and fatigue properties was discussed. Based on the dislocation annihilation mechanisms, the fatigue life model considering dislocation annihilation was established. When the ratio of (rho) over bar (-) to (rho) over bar increased, the fatigue life increased. Therefore, for cyclic hardening materials, obvious dislocation annihilation can increase fatigue life.
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