New Aspects of Gas-Induced Swelling in Helium-Implanted Nickel during Annealing

We review results of an extensive study on bubble coarsening in nickel and provide some useful additional data which round off our picture deduced from the combined experimental evidence and from theoretical considerations: During annealing the bubble structure near the surface and near grain boundaries coarsens faster than in the bulk, leading to separated populations of large and small bubbles, respectively. The coarsening mechanism of the large bubbles near boundaries is identified as Ostwald ripening, whereas in the bulk coarsening proceeds by slow migration and coalescence, i.e. the bulk bubbles remain small and keep their overpressure.