| Zirconium alloys are employed extensively in light water cooled reactors (LWR) as the cladding materials of fuel elements and other structural materials because of the low capture cross-section for thermal neutrons, good resistance to water-side corrosion at elevated temperature, adequate mechanical properties and high thermal conductivity. The power fluctuation and flow-induced vibration make the fuel assembly and other components deformed cyclically under the LWR operating condition, even failed in the severe cases. It is therefore necessary to have an accurate knowledge of low-cycle fatigue (LCF) behavior demonstrated by zirconium alloys in order to run the reactor safely, and it becomes in immediate need of the detailed knowledge when the new fuel assembly in request is being developed to reduce the cost of nuclear electricity.In this dissertation, the effect of texture, heat-treatment, and hydrogen on the LCF behavior of Zircaloy-4 and the cyclic deformation behavior for Zircaloy-4, N18 alloy and N36 alloy have been investigated systematically using fully-reversed tension-compression loading under strain control (R =min/max =-1), while the evolvement of the friction and back stresses versus the number of repeated working cycles and the plastic strain amplitude has been studied, and the thorough discussioncombined with the analysis result of fatigue sub-structure, friction and back stresses, and fatigue fracture has been given to the mechanism underlying the LCF behavior of alloys.The investigation for the LCF behavior of Zircaloy-4 with different metallurgical conditions at room temperature and 400 indicates that the LCF life(Nf) always decreases with increasing the range of plastic strain p and obeys the Coffin-Manson relation Nf sp = C. However, different metallurgical conditions of the alloy contribute to different LCF properties. Zircaloy-4 sheet, which was cold-worked followed by recrystallization annealing, exhibits longer LCF life in the rolling direction than that in the transverse direction, and the fact that difference in LCF life between both directions becomes larger as the range of plastic strain becomes lower can be attributed to the texture effect, p-solution treatment deteriorates the alloy's LCF property because the treatment lowers the average value of alloy's Schmid factors, and the subsequent annealing-treatment in a-phase range has a impact on the LCF properties, i.e. the subsequent annealing-treatment at 500癈 for 1.5h results in better property than that at 750 for 1.5h, which comes mainly from the fact that the alloy annealled at 500 for 1.5h has lower amount of the precipitate particles than the alloy annealled at 750 for 1.5h. 240 g/g hydrogen improve effectively the alloy's LCF property because the solute hydrogen in the a-matrix (~200g/g) cheapens the interaction between dislocation and solute atoms, and pinning points, thus leading to speedup of dislocation emission and enhancement of dislocation mobility.The cyclic deformation behavior for Zircaloy-4, N18 alloy and N36 alloy at room temperature and 400 has been investigated in a single-sample test or multi-sample test. The results indicate that the relationship between the saturated stress (,.) and the plastic strain amplitude (sp) both at room temperature and 400 can be expressed by a power law relation s = Ksepns . The alloys, which were cold-worked followed by recrystallization annealing, display cyclic softening in the range of low strain because the cyclic stress-strain curve lies below the monotonic stress-strain curve, and show cyclic hardening in the range of high strainbecause the cyclic stress-strain curve lies above the monotonic stress-strain curve. For the cyclic deformation under a given strain at room temperature, cyclic softening is usually displayed till to failure in the lower range of strain; However, cyclic hardening is displayed in the early stage in the higher range of strain, subsequent cyclic softening in the later stage and till to failure. Dynamic strain ageing (DSA) appears...
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