The effect of iron on dislocation evolution in model and commercial zirconium alloys - 2016-0068
Although the evolution of irradiation-induced dislocation loops has been well correlated with irradiation-induced growth phenomena, the effect of alloying elements on this evolution remains elusive, especially at low fluences. To develop a more mechanistic understanding of the role iron has on loop formation, we used state-of-the-art techniques to study a proton-irradiated Zr-0.1Fe alloy and proton- and neutron-irradiated Zircaloy-2. The two alloys were irradiated with 2-MeV protons up to 7 dpa at 350 deg. C and Zircaloy-2 up to 14.7 X 10{sup 25} n. m{sup -2}, approximately 24 dpa, in a boiling water reactor at approximately 300 deg. C. Baseline transmission electron microscopy showed that the Zr{sub 3}Fe secondary-phase particles in the binary system were larger and fewer in number than the Zr(Fe,Cr){sub 2} and Zr{sub 2}(Fe,Ni) particles in Zircaloy-2. An analysis of the irradiated binary alloy revealed only limited dissolution of Ze{sub 3}Fe, suggesting little dispersion of iron into the matrix, while at the same time a higher -loop density was observed compared with Zircaloy-2 at equivalent proton dose levels. We also found that the redistribution of iron during irradiation led to the formation of iron nano-clusters. A delay in the onset of -loop nucleation in proton-irradiated Zircaloy-2 compared with the binary alloy was observed. The effect of iron redistributed from secondary-phase particles because of dissolution on the density and morphology of and loops is described. The implication this may have on irradiation-induced growth of zirconium fuel cladding is also discussed. (authors)