Anomalous helium bubble diffusion in dilute aluminium alloys

Remarkably rapid Brownian motion of helium bubbles in Al alloyed with very low concentrations of Pb and of indium has been observed in situ by hot-stage transmission electron microscopy. Bubble diffusion is enhanced as the impurity coats the bubble surfaces at annealing temperatures above the melting point of the impurity. The bubble diffusion coefficients calculated from video images of the bubble motion, and the corresponding surface diffusion coefficients, are orders of magnitude larger than diffusion coefficients determined from He bubble growth experiments in pure Al.