Abstract
Wrought Zircaloy-2 and Zircaloy-4 were neutron irradiated at nominally 358 C in the high flux isotope
reactor (HFIR) at relatively low neutron fluences between 5.8 1022 and 2.9 1025 n/m2 (E > 1 MeV). The
irradiation hardening and change in microstructure were characterized following irradiation using tensile
testing and examinations of microstructure using Analytical Electron Microscopy (AEM). Small increments
of dose (0.0058, 0.11, 0.55, 1.08, and 2.93 1025 n/m2) were used in the range where the
saturation of irradiation hardening is typically observed so that the role of microstructure evolution
and hai loop formation on irradiation hardening could be correlated. An incubation dose between
5.8 1023 and 1.1 1024 n/m2 was needed for loop nucleation to occur that resulted in irradiation hardening.
Increases in yield strength were consistent with previous results in this temperature regime, and
as expected less irradiation hardening and lower hai loop number density values than those generally
reported in literature for irradiations at 260–326 C were observed. Unlike previous lower temperature
data, there is evidence in this study that the irradiation hardening can decrease with dose over certain
ranges of fluence. Irradiation induced voids were observed in very low numbers in the Zircaloy-2 materials
at the highest fluence.
