Abstract
The efforts of many scientists for more than a half of a century have resulted in a
substantial understanding of the response of Zr-based materials to irradiation.
However, the models of radiation growth proposed to date have not played a
decisive role in creating radiation-resistant materials and cannot predict strain
rates at high irradiation doses. The main reason for this is the common
assumption that, regardless of the incident particle mass and energy, the
primary damage consists of single vacancies and self-interstitial atoms (SIAs),
both diffusing three-dimensionally. Thus, the models ignore the distinguishing
features of the damage production in displacement cascades during fastparticle,
e.g., neutron, irradiation; namely, the intra-cascade clustering of
vacancies and SIAs and one-dimensional diffusion of SIA clusters. Over the last
twenty years or so, the production bias model (PBM) has been developed, which
accounts for these features and explains many observations in cubic crystals.
The cascades in hcp crystals are found to be similar to those in cubic crystals;
hence one can expect that the PBM will provide a realistic framework for the hcp metals as well. It is shown in this paper that it reproduces all the growth stages
observed in annealed materials under neutron irradiation, such as the high strain
rate at low, strain saturation at intermediate, and breakaway growth at relatively
high doses. It accounts for the striking observations of negative strains in
prismatic directions and co-existence of vacancy- and interstitial-type prismatic
loops, which have never been explained before. It reveals the role of cold work in
the radiation growth behavior and the reasons for the alignment of basal
vacancy-type loops along the basal planes. The critical parameters determining
the high-dose behavior are revealed and the maximum growth rate is estimated.
