Study On Low-Cycle Fatigue Behavior Of Zircaloy-4

Low cycle fatigue (LCF) behavior of Zircaloy-4 has been reviewed in the present paper. Then, the LCF behavior of a recrystallized Zircaloy-4 plate with different texture has been studied at room temperature and 400℃, respectively. Furthermore, the LCF behavior of hydrided Zircaloy-4 plate has been also investigated. And finally, SEM has been used to characterize the fracture.The results indicate that the relationship between the fatigue lifetime and cyclic plastic strain range obeys Coffm-Manson relation, and the relation between the hysteresis energy (Wn) and the plastic strain range (εp) can be described by a power-law: WH=hεPw.The low-cycle fatigue behavior of R specimen is better than that of T specimen at room temperature. It can be noticed that both R and T specimens show initial hardening and subsequent softening at the strain amplitude higher than 0.8% and cyclic softening from the beginning to fracture under strain amplitude less than 0.8% at room temperature, and the cyclic flow stress was always lower in R specimen than in T specimen at the same strain range. In addition, the cyclic softening under the strain amplitude less than 0.8% can be explained by "grain-rotation induced cyclic softening", and the cyclic hardening in the higher strain amplitude was attributed to twinning.The LCF behavior of a recrystallized Zircaloy-4 plate at room temperature and 400℃ show that alloy has better LCF property at RT than at 400℃, and cyclic hardening at 400℃ which could be attributed to the dynamic strain aging effects.It is noticeable that the hydrided plate has the same cyclic behavior as the above unhydrided sample at room temperature. However, The LCF of R specimen containing -200μg /g hydrogen is better than that of the hydrided T specimen, and shows slightly superior to unhydrided R specimen, whereas the hydrided T specimen has not the apparent difference as compared with T specimen.SEM investigation shows that all the crack initiations can be traced back to the lateral sides of the sample, and the crack propagates along the direction normal to the loading axis. There exists pronounced difference in the fatigue fracture at room temperature and 400℃. At room temperature, the fracture for R specimen is the characteristic of fatigue stripe, while tire-like pattern appears on the fracture of the T specimen, and the hydrided sample is characterized by skeleton-like pattern and quasi-cleavage fracture at room temperature. However, the fracture characterized by second-crack at 400℃.