Object kinetic Monte Carlo study of sink strengths

The sink strength for three-dimensionally (3D) versus one-dimensionally (1D), or mixed 1D/3D, migrating defects in irradiated materials has attracted much attention in the recent past, because many experimental observations cannot be interpreted unless 1D or mixed 1D/3D migration patterns are assumed for self-interstitial atom clusters produced in cascades during irradiation. Analytical expressions for the sink strengths for defects migrating in 3D and also in 1D have been therefore developed and a 'master curve' approach has been proposed to describe the transition from purely 1D to purely 3D defect migration. Object kinetic Monte Carlo (OKMC) methods have subsequently been used to corroborate the theoretical expressions but, although good agreement was generally found, the ability of this technique to reach the 1D migration limit has been questioned, the limited size of the simulation box used in OKMC studies having been mainly blamed for the inadequacies of the model. In the present work, we explore the capability of OKMC to reproduce the sink strengths of spherical absorbers in a wide range of volume fractions, together with the sink strength of grain boundaries, for defects characterised by different migration dimensionality, from fully 3D to pure 1D. We show that this technique is not only capable of reproducing the theoretical expressions for the sink strengths in the whole range of conditions explored, but is also sensitive enough to reveal the necessity of correcting the theoretical expressions for large sink volume fractions. We thereby demonstrate that, in spite of the limited size of the OKMC simulation box, the method is suitable to describe the microstructure evolution of irradiated materials for any defect migration pattern, including fully 1D migrating defects, as well as to allow for the effect of extended microstructural features, much larger than the simulation box, such as grain boundaries.