Development of microstructure and irradiation hardening of Zircaloy during low dose neutron irradiation at nominally 377-440 °C

Neutron irradiation of wrought Zircaloy-2 and Zircaloy-4 was performed in the Advanced Test Reactor (ATR) at irradiation temperatures of nominally 377-440 °C to relatively low neutron fluences between 3 and 31 × 1024 n/m2 (E >1 MeV). The irradiation hardening was measured using tensile testing. For this relatively high application temperature (377-440 °C) saturation of hardening was observed at the relatively low dose of 3 and 8 × 1024 n/m2, but the magnitude of irradiation hardening is much less than reported in the literature for lower irradiation temperatures of 260-326 °C. Examinations of microstructure were used to show that a lower number density of 〈a〉 loops is present that results in the lower level of irradiation hardening. The lower irradiation hardening for the higher irradiation temperature is consistent with literature data. The amorphization of Zr(Fe,Cr)2 precipitates and resulting change in precipitate composition during irradiation is characterized, and the potential role of these effects on 〈a〉 loop and 〈c〉 loop formation and irradiation hardening is discussed.