Saturation Of Swelling Research Articles

Inhomogeneous Swelling Near Grain Boundaries in Irradiated Materials: Cavity Nucleation and Growth Saturation Effects

ABSTRACTThe effect of inhomogeneous nucleation and growth of cavities near grain boundaries illustrates the failure of the standard rate theory to describe the kinetics of phase transformations in irradiated materials under cascade damage conditions. The enhanced swelling observed near grain boundaries is believed to result from the competition between the diffusional growth of cavities and their shrinkage due to the interaction with mobile interstitial clusters. Swelling rates associated with the two processes behave in a radically different way as a function of the size of growing cavities. For a spatially homogeneous distribution of cavities this gives rise to the saturation of swelling in the limit of large irradiation doses.We investigate the evolution of the population of cavities nucleating and growing near a planar grain boundary. We show that a cavity growing near the boundary is able to reach a size that is substantially larger than the size of a cavity growing in the interior region of the grain. For a planar grain boundary the magnitude of swelling at maximum is found to be up to eight times higher than the magnitude of swelling in the grain interior.

Saturation of swelling in neutron-irradiated molybdenum and its dependence on irradiation temperature and starting microstructural state

Molybdenum and its alloys are of interest for potential fusion application due to their high melting points and relatively good thermal conductivities. The development of void superlattices during neutron irradiation appears to limit void swelling in pure molybdenum to values below 4% over a wide range of irradiation temperatures. The saturation value of swelling and the void superlattice parameter each appear to be somewhat dependent on temperature, but independent of the thermomechanical starting state. Formation of technetium and ruthenium by transmutation may also play some minor role in the microstructural evolution, but do not appear to be involved in the limitation of swelling observed in this and other experiments.

Some implications of anisotropic self-interstitial diffusion on void swelling in metals

Earlier work has suggested the probable role of two-dimensional diffusion of self-interstitial atoms (SIA) in the phenomena of void, bubble and vacancy loop lattice formation in metals. In the present paper other consequences of 2-D SIA diffusion are examined. These include enhanced void swelling rates at low displacement doses and the later saturation of swelling, boundary effects and correlated recombination of SIA and vacancies.