| Though it has long been appreciated that materials differ in their response to heavy-ion irradiation, the reasons for this are not yet fully understood. To more fully characterize the effects of material, alloying element, irradiation temperature and ion dose on the probability of collapse of a displacement cascade, Cu, Ni, and dilute Ni alloys (Ni-Si and Ni-Al) have been irradiated with 50 and 100 keV heavy-ions (Kr{dollar}sp+{dollar} and Ni{dollar}sp+{dollar}) at both 30 and 300K, and to doses ranging from 10{dollar}sp{lcub}15{rcub}{dollar}-10{dollar}sp{lcub}17{rcub}{dollar} ions m{dollar}sp{lcub}-2{rcub}{dollar}. The irradiations resulted in the formation of vacancy dislocation loops which were examined in a transmission electron microscope (TEM) and characterized by their size, Burgers vector, and formation probability. For some of the irradiations, the HVEM-Accelerator Facility and Argonne National Laboratory was used. This facility is unique in that it allows irradiation and microstructural examination to be performed at temperatures where there is no long-range point defect mobility and the examination of the same area of sample at different dose levels.; It was found that in Cu irradiated with 50 keV Kr{dollar}sp+{dollar} ions at 300K, a displacement cascade collapses to a dislocation loop with a higher probability and creates a larger loop than in Ni. This difference, which indicates that the cascade efficiency is higher in Cu, is maintained for irradiations at 30K, but the probability for collapse is decreased in both metals relative to the 300K irradiations. This decrease in collapse probability with temperature was also seen in the dilute Ni alloys examined.; The addition of dilute amounts of Si and Al to Ni changes the irradiation response in a complex manner. The collapse probability at 300K initially increases with the addition of Si or Al, then decreases at higher concentrations. There is no significant difference in the collapse probability of the alloys at 30K.; As the ion dose was increased in all materials, some loops disappeared while others moved, changed size, or changed their Burgers vectors. This behavior is attributed to the overlap of fresh cascades on pre-existing dislocation loops causing them to disappear or be altered.; The vacancy agglomeration model that is found to best account for these experimental observations is the molten zone model. This model, which stems from Molecular Dynamics computer simulations of cascades, submits that the central zone of the displacement cascade melts, and the resolidification process results in the clustering of vacancies. |
