Precipitates in zircaloy: Identification and the effects of irradiation and thermal treatment

The effects of thermal treatment and neutron irradiation on precipitates in Zircaloy have been investigated by analytical electron microscopy. Intermetallics Zr(Fe, Cr)2 and Zr2(Fe, Ni) are the major precipitates in α-recrystallized Zircaloy-2 and Zr(Fe, Cr)2 is the major precipitate in Zircaloy-4. Zr-silicide and Zr-Cu-sulfide are minor precipitates and amorphous inclusions, respectively. In Zircaloy heat treated in the α + β- or β-phase fields, fine platelet Zr4(Fe, Cr) precipitates decorate the boundaries of lamellae formed on quenching. Neutron irradiation results in a change from a crystalline to an amorphous structure in the Zr(Fe, Cr)2 precipitates. The amorphous transformation starts at the periphery of the precipitate and the thickness of the amorphous ring increases as the fluence increases. The process leading to amorphization is discussed based on the effects of irradiation-induced point defects. In α + β- or β-heat-treated Zircalioy, the fine Zr4(Fe, Cr) precipitates are completely dissolved into the matrix upon irradiation.