On the transfer of cascades from primary damage codes to rate equation cluster dynamics and its relation to experiments

Abstract

Transferring displacement cascades from primary damage codes to rate equation cluster dynamics (RECD) is not straightforward, due to the inability of RECD to treat spatial correlations explicitly. A method, called ''sphere homogenization kinetic Monte Carlo" (SHKMC), has been proposed to produce a effective source term from a cascade database. This paper reviews the method and a few applications. SHKMC is based on a modified kinetic Monte Carlo algorithm to keep track of the homogenization process of defects within cascades. The crucial parameter is the homogenization distance, which is not an intrinsic parameter of cascades but which is given by RECD simulations. SHKMC leads to a time-varying source term, even under constant irradiation flux. RECD with such a source term is able to reproduce reference kinetic Monte Carlo calculations of microstructure evolution under cascade conditions. It is also possible to provide a spatially-dependent source term for the simulation of ion irradiations. As an example, irradiation of iron with 10 MeV Fe ions is discussed. Analysis of the source term shows that the fraction of mono-defects is close to the fraction of freely-migrating defects determined experimentally and that it significantly varies with depth.

Effect of sink strength dispersion on cluster size distributions simulated by cluster dynamics

“…Under thermal aging, CD reproduces well AKMC results provided it is carefully parametrized with the same atomistic data [2,3] and that potential corrections are added to the classical formalism to handle concentrated alloys [7,8]. For materials under irradiation, it has been shown that provided input parameters in CD and OKMC are consistent, cluster size distributions are very similar for low volume fractions, even if distributions obtained with OKMC can be slightly broader than those obtained with CD [9]. Tests at higher volume fractions have not been performed, to our knowledge.…”

Kinetic Monte Carlo Simulations of Irradiation Effects

“…These models are thus capable of providing relevant information that closer to real materials. However, these simulations require that a large number of parameters (and the way they evolve with temperature) be known accurately, not to mention the impact of surfaces (Aliaga et al 2016) (Duan et al 2018) or the source term, as recently shown in (Jourdan and Crocombette 2018). This means that considerable effort must go into choosing the level of details to enter in the models to minimally perturb the results.…”

“…In some very specific cases, it is possible to neglect some of the point defect reactions thus speeding up the calculations as was shown by (Pelaz et al 2007) in ion implanted Si, but in general one must account explicitly for both point defect populations. Furthermore, the very recent study by Jourdan et al (Jourdan and Crocombette 2018) shows that the cascade annealing depends on the point defect concentrations and must thus be evaluated on-the-fly or for different point defect concentrations unlike it has been typically done. The main outcome of all these studies is to point out as in the previous section that it is necessary to have a better understanding of how the point defect and point defect clusters mobilities are affected by solutes, temperatures and other point defects.…”

European materials development: Results and perspective

“…The relaxation and evolution of the damage produced by cascade events occurs at comparatively long timescales, often comparable with the interval of time between the subsequent cascade events, especially in the low dose rate limit. The models that are being explored here span the interval from stochastic kMC approaches [35] to diffusion-mediated dislocation based models [36] to rate theory cluster dynamics type simulations that are expected to be able to help explain the observed evolution of radiation induced microstructures [37].…”