Abstract
The production of vacancy loops by the collapse of displacement cascades is of particular importance in radiation damage, for these loops are known to play a major role in subsequent microstructural development, and yet little is known of the cascade processes in them. In this study, attention has been focused on cascade collapse to form vacancy loops in five of the h.c.p. metals, namely Ti, Co, Re, Ru and Mg, chosen for their wide-ranging material properties. Sb+ ions of either 100 of 150 keV have been used to produce cascades, which may collapse to form vacancy dislocation loops. These loops have been studied using transmission electron microscopy, and this has enabled detailed analysis to be undertaken of loop geometry, size and number density. For the foil orientation used, all the loops observed lay on the prism planes, and from the size distributions of faulted and perfect loops we have estimated values for the prism plane stacking-fault energy.
The efficiency of collapse varies dramatically for the five metals studied, but these variations do not correlate simply with material parameters such as melting point, c/a ratio, stacking-fault energy or atomic weight. In Ti the probability of visible vacancy loop production is very low, and this contrasts with Co, a material of similar atomic weight and melting point, where a significant proportion of the vacancies created are retained in visible loops (about 10%). Ru and Re also exhibit a relatively high retention efficiency of 5–10%, but it is negligible in Mg. The data collected from this study demonstrated the complexities of the processes involved in cascade formation.
