In-situ observation of the migration and growth of helium bubbles in aluminum

Brownian motion of helim bubbles, their disappearance, and coalescence in high purity aluminum were demonstrated in real time by electron microscopy and the recording of these whole processes on VTR. It was experimentally established for the first time that the mean square of the migration distance of the bubble during the time duration, t, is proportional to t at least for t ≥ 1 min. The growth of the bubble was caused by the coalescence between bubbles during Brownian motion and also by annealing at higher temperature unless the coalescence takes place. A dependence of the diffusivity of the bubble on its diameter and a rapid formation of new bubble by the coalescence of two bubbles seem to be supported through the surface diffusion of aluminum on the bubble surface. (orig.)