The microstructural evolution of Zircaloy-4 subjected to proton irradiation

Various thermo-mechanically treated Zircaloy-4 specimens which were subjected to 1 MeV H+ irradiation at 350deg C up to a total dose of 1 dpa were studied by transmission electron microscopy (TEM). It was observed that the proton-irradiation has a great effect on the microstructural evolution in this alloy. In β-quenched specimens, the original fine ZrFe2 (fcc) particles which were decorated along the lamellae boundary were gradually dissolved following the subsequent thermo-mechanical treatment or by the proton irradiation. Radiation-enhanced precipitate coarsening was observed for the Zr(Cr, Fe)2 (hcp) precipitate phase after irradiation. In β-annealed specimens, the starting phase of the precipitates was identified as a complex structure (hcp and fcc) Laves phase of Zr(Cr, Fe)2. Proton irradiation enhanced the phase transformation from the C14 (hcp) phase to the C15 (fcc) phase. A new phase was also occasionally observed in one type of specimens, B6, irradiated to 1 dpa. This phase was identified as Zr4Sn (tetragonal) phase. It is concluded that after a long time exposure, the microstructural evolution of Zircaloy-4 cladding material will be dominated only by irradiation. (orig.)