In-situ observation of Brownian motion of helium bubbles along grain boundaries in aluminium

Abstract

The diffusion profile of small helium bubbles along grain boundaries in in-situ aluminium has been examined by electron microscopy observation. It was found that bubbles moved two-dimensionally in the general grainboundary interface with a misorientation about the axis [122]. The occurrence 2 * ) ( P R t probability, of the square of the bubble migration distance along the x boundary can be well fitted to a relation of the random-walk theory. The mean 2 R square of the migration distance is proportional to the time which is required x to move the distance. These facts provide clear quantitative evidence of Brownian-type motion of the bubble along the grain boundary and yield -18 2 1 D the bubble diffusivity; for example, = 5.6 10 m s at 833 K for a bubble of diameter 2.3nm. The diffusivity obtained is much higher than that in the lattice matrix.