Amorphization of precipitates in Zircaloy under neutron and charged-particle irradiation

The crystalline-amorphous transformation of the intermetallic precipitates Zr(Cr,Fe)₂ and Zr₂(Ni,Fe) in Zircaloy under charged-particle and neutron irradiation is studied. In the first section, the experimental results in the literature are reviewed for the three types of irradiation; neutron, electron, and ion. It is found that the dose to amorphization in all three types of irradiation exhibits roughly the same exponential dependence with temperature but that there are important differences. The critical temperatures, above which amorphization is not practically attainable, are different for each type of irradiation, indicating the presence of different damage accumulation and annealing mechanisms in each case. Further evidence of this are the different amorphization morphologies observed under neutron and electron irradiation, and the shift in the relative susceptibility to amorphization between the two types of precipitate under high (neutron and ion) and low (electron and ion) temperature irradiation. In the next section, the theoretical models for amorphization are reviewed and applied to the problem in an effort to obtain a coherent picture of amorphization induced by all types of irradiation in the precipitate/zirconium system. Amorphization mechanisms are proposed for each type of irradiation, based on the experimental results. A brief conclusion indicates that different mechanisms are operative for amorphization induced by each type of irradiation and points out future areas that in our view deserve further investigation.