On the relative contributions of point defect clusters to macroscopic swelling of metals

This paper is part of the Special Topic on Radiation Effects in MaterialsInternational audienceSwelling of metals under irradiation is commonly assessed by calculating the volume fraction of voids, which appear at temperatures where vacancies are mobile. However, other clusters are formed, which may also have an impact on swelling. In particular interstitial loops have recently been considered to give a significant contribution to swelling owing to their large relaxation volume. In this work we perform calculations in nickel, based on interatomic potentials, to estimate the contributions of the various point defect clusters. We show that voids produce much more swelling than loops and stacking fault tetrahedra, whose contribution is essentially due to the dislocation core field, inducing a dilatation per unit length of around 1$b^2$, where $b$ is the Burgers vector. Evaluation of swelling should indeed be done by summing formation volumes, not relaxation volumes, the latter being related to lattice parameter change as measured by X-ray diffraction. We also discuss the case of ``lattice swelling'' occuring when vacancies are immobile. When self-interstitial atoms cluster as dislocation loops, this swelling mode turns out to be nothing but ``void'' swelling in a regime where vacancy mobility is so low that vacancies do not cluster appreciably, leaving only interstitial loops visible in transmission electron microscopy