Abstract
A model is presented for the migration of cavities in crystals. Although individual mechanisms of cavity migration have been considered previously, it has proved necessary to produce more accurate analytical solutions. Considerable attention has been given to how the individual mechanisms combine. The results of this analysis have been compared to previously obtained experimental results on cavity migration in copper, uranium dioxide and stainless steel. This comparison showed that the model was reasonably accurate and enabled several conclusions to be drawn. Two of these conclusions were that cavity migration occurs predominantly by surface diffusion and that a dense gas inside a cavity will impede its migration. Cavity growth has also been studied. Cavity distributions produced by the implantation of 500keV helium into nickel and subsequent heat treatments were studied by cross-sectional TEM by Mr N. Marochov. I have modelled the development of the cavities on annealing. This cavity growth could only be accounted for in terms of both migration and coalescence and vacancy supply from the surface. The migration of small cavities was inhibited by the high gas density in these cavities. The implications of these observations on the interpretation of cavity growth experiments are discussed. Cavity growth mechanism maps are presented for cavity growth in niobium, nickel and uranium dioxide under widely varying conditions. Maps are potentially very useful because they enable the growth mechanism and rate to be predicted in regimes where experiments are difficult or impossible. The importance of the quality of the data is emphasized and the prospects for this technique are discussed.