Effects of heterogeneous sink distribution on void swelling

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Abstract
Swelling rates are calculated for two types of material with heterogeneous distributions of dislocations and voids, namely copper irradiated with neutrons to low dose at 250°C and heavily cold-worked copper irradiated with 1 MeV electrons in a HVEM at 250°C. Both materials are considered to consist of non-interacting spherical components with a wall and an inner cell with different dislocation and/or void densities. We subdivide the sphere (wall plus cell) in a number of concentric shells and find a quasi-static solution for the interstitial and vacancy concentrations in the different shells by a finite-difference method. From these concentrations the local and the average swelling rates are calculated. The effect of the heterogeneities in sink distribution on swelling rate and the dependence of this effect on various structural parameters are investigated. We find that a heterogeneous sink distribution may increase or decrease the swelling rate relative to the swelling rate for a homogeneous distribution of the sinks depending on the structural parameters and the irradiation conditions. For neutron-irradiated copper neither the calculated swelling rate nor its spatial variation agree with the experimental observations. For cold-worked copper, on the other hand, there is reasonable agreement between calculations and experiments.