The growth of inert gas bubbles within grains and at grain boundaries - a comparison of mechanisms

A brief survey is presented of mechanisms by which inert gas bubbles may grow and it concentrates on those processes, not directly dependent on irradiation, which can cause rapid growth, including the situations where the gas pressure may exceed, be equal to, or be less than the surface energy restraint. The importance of bubble coalescence is emphasised. This occurs only to a very small extent by purely random motion but is much more strongly dependent on the response of bubbles to driving forces whereby their movement can be greatly increased. Bubbles situated on grain boundaries are subjected to a greater variety of driving forces than those within grains and those caused by grain boundary movement or directly by the action of stress are especially important. The sensitivity to stress system as well as magnitude is a particular feature and this relates to the anisotropy of overall shape changes, to gas release and to fracture. (author)