Cavity nucleation during post-irradiation creep

During the post-irradiation annealing of metals at high temperatures small nanometer-sized bubbles are observed to form. The bubbles are thought to be responsible for the low ductility observed during post-irradiation creep although they are too small to grow directly by the action of the applied stress. The present paper discusses the sweeping of bubbles on climbing dislocations and the binding to dislocations and grain boundaries. A model is developed describing the kinetics of bubble sweeping to grain boundaries during creep. Bubbles accumulate on the boundaries and coalesce. The theory is compared with measurements made on a precipitate-free stainless steel. It is shown that the strain required to nucleate creep cavities by this mechanism is small at high stresses but can become large at very high temperature and low stresses. (orig.)