The crystalline-amorphous transformation of the intermetallic precipitates Zr2 (Fe, Ni) and Zr(Cr, Fe)2 in Zircaloy under irradiation is studied. Experiments show that the dose-to-amorphization increases exponentially with temperature and decreases with dose rate. A model for the transformation is proposed that accounts for these observations. In this model amorphization is caused by the destabilization of the crystalline phase with respect to the amorphous phase caused by an irradiation-induced increase in its free energy. Contributions to the free energy increase due to both point defect increases and irradiation-induced-disordering are calculated and found to have approximately the same magnitude. The disordering contribution is independent of temperature and dose rate, since thermal reordering is small compared to ballistic disordering for the temperatures of interest. The temperature and dose rate dependences of the dose-to-amorphization are given by the point defect contribution. This indicates that electron-irradiation-induced amorphization is caused not only by irradiation-induced disordering but also by an increase in point defect concentration. A simplified version of the model valid at high temperature finds that the controlling parameter for amorphization is the parameter dpa.k 1 2, where dpa is the dose and k the dose rate. This model is then compared with other models in the literature on the basis of amorphization kinetics and of the temperature and dose rate dependence of the dose-to-amorphization. The characteristics of the amorphous transformation under electron irradiation and neutron irradiation are discussed. It is believed that different amorphization mechanisms are operative in each case.
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