Role of dislocation loops in the development of vacancies-containing cavities

This paper presents the results of a TEM-investigation of the effect of postradiation annealing on the structure of molybdenum doped with helium atoms and irradiated with high-energy α-particles and fission neutrons. It was found that: the number of the interstitial atoms in the dislocation loops and of the vacancies in the helium bubbles increases with an increase in the temperature and annealing time, that is, the dislocation loops grow by emitting vacancies; the arising and growth of helium pores involves a stage characterised by the growing of vacancy voids; the helium bubbles arising near grain boundaries are formed on the side of the grain body with dislocation loops; the postradiation annealing of the structure involving dislocation loops produced by irradiation with 50 MeV α-particles and fission neutrons at 60 deg C results in the development of vacancy voids. The foregoing gives grounds to state that high temperature annealing or irradiation at high temperature (more than 0.3 Tmelt.) constitutes the conditions under which dislocation loops are powerful sources of vacancies. Therefore, on condition that in the crystal structure of the irradiated material there are, for example, the HemVn complexes, vacancy oversaturation accounted for by thermal emission of vacancies by dislocation loops of radiation origin may be the main driving force for the nucleation and growth of vacancy voids. (author)