The formation of defect clusters in samples which had been bombarded with He+ ions was studied. Wedge-shaped specimens were bombarded with the ions (20 to 100keV) at temperatures of between 300 and 570K. It was concluded that the small fraction of damage cascades that was introduced by the He ions led to the direct nucleation of vacancy and interstitial clusters. High-energy primary knock-on atoms not only produced vacancy clusters via the collapse of displacement cascades (especially near to sinks), but also provided nuclei for interstitial loops. The He atoms stabilized perfect loops rather than Frank loops with stacking faults, and increased the stacking fault energy of both metals. It was also noted that the threshold energy for the formation of vacancy clusters was slightly higher for Ni than for Cu.

J.Shimizu, K.Yasuda, C.Kinoshita: Journal of Nuclear Materials, 1994, 212-215[A], 207-11