Inhomogeneous Swelling Near Grain Boundaries in Irradiated Materials: Cavity Nucleation and Growth Saturation Effects
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Inhomogeneous Swelling Near Grain Boundaries in Irradiated Materials: Cavity Nucleation and Growth Saturation E ects S. L. Dudarev EURATOM/UKAEA Fusion Association Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, England, U.K. ABSTRACT
The e ect 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 di usional 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 di erent 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. INTRODUCTION
Clustering of defects in collision cascades in a material irradiated by high-energy particles (for example, by 14.1 MeV neutrons in a fusion power plant) gives rise to a new mode of microstructural evolution that does not occur under electron irradiation in a high-voltage electron microscope. Molecular dynamics (MD) simulations show that for an individual interstitial atom the equilibrium dumbbell con guration (shown in Figure 1 below) is characterized by the comparatively low level of thermally activated mobility. A dumbbell defect moves through the crystal lattice via a sequence of thermally activated hops separated by relatively long intervals of time during which the defect resides on a particular lattice site [1]. On the other hand, clusters of interstitial atoms form equilibrium glissile con gurations similar to those shown in Figure 2 and characterized by a considerably higher degree of thermal mobility. The latter conclusion appears to
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be largely independent of the choice of the interatomic interaction potential used in a MD simulation [2], and it has a signi cant bearing on the kinetics of evolution of the microstructure of irradiated materials on the mesoscopic scale.
Equilibrium con gurations of interstitial atom defects in the body-centered lattice of iron. The h110i dumbbell con guration shown on the left is characterized by the energy of formation E = 4:876 eV, which is lower than the energy of formation of the h111i crowdion con guration shown on the right where E = 5:004 eV. These numerical values were obtained using the many-body potential developed by Ackland et. al., and agree with res
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