Kinetic Monte Carlo Annealing Simulation of Cascade Damage in α-Fe (Selected Papers of the Joint International Conference of Supercomputing in Nuclear Applications and Monte Carlo : SNA + MC 2010) (original) (raw)
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Kinetic Monte Carlo Annealing Simulation of Cascade Damage in α-Fe
Progress in Nuclear Science and Technology, 2011
Molecular dynamics is a useful tool for simulating cascade damage in metals and alloys, but the time scale accessible to molecular dynamics is only about 10-10 s. Kinetic Monte Carlo can be used to simulate annealing of cascade damage to permit analysis of the longer time evolution of cascade damage. We conducted a series of such annealing simulations in α-Fe. The number of surviving displacements before annealing is ~0.3 of the Norgett-Robinson-Torrens (NRT) value in the case of primary knock-on atoms with energy more than ~10 keV, and it decreased by ~30% during the annealing at 300 K because of recombination of vacancies and self-interstitial atoms. The recombination ratio increased as the annealing temperature increased. These results can be meaningfully applied in models such as mean field reaction rate theory used to simulate long-term radiation damage accumulation. We also demonstrated that 1D motion of small SIA clusters can substantially influence the long-term accumulation of cascade damage.
Philosophical Magazine, 2005
We describe a series of kinetic Monte Carlo simulations of post-cascade radiation damage evolution in -iron that illustrates the part played by elastic interaction between defects. Elastic interactions are included as a bias to the diffusion of mobile point defects and defect clusters. The simulations show that recombination fractions are reduced, and vacancy clustering is enhanced. The sensitivity of these effects to temperature, cascade energy, and geometric description of vacancy clusters is also investigated.
Journal of Nuclear Materials, 2006
Kinetic Monte Carlo is used extensively in the field of radiation effects to understand damage accumulation and growth under irradiation. These calculations require previous knowledge on the formation of these defects, the relative stabilities of the different types of defects, their interactions and their mobilities. Many of these parameters can be extracted from molecular dynamics calculations using empirical potentials or from ab initio calculations. However, the number of parameters necessary for a complete picture is rather large. Kinetic Monte Carlo can be used as a tool to isolate those parameters that most influence the outcome of the calculations. In this paper, we focus on one aspect: the form of the damage after the collision cascade. We describe the effect of the form of the cascade as obtained from molecular dynamics simulations on damage accumulation. In particular, we demonstrate that the form of the cascade drastically changes the nucleation and growth of helium-vacancy clusters, possible precursors of voids and bubbles. Finally, we point to those open questions that need to be resolved to develop a truly predictive kinetic Monte Carlo model.
The primary damage in Fe revisited by Molecular Dynamics and its binary collision approximation
MRS Proceedings, 2000
Molecular Dynamics (MD) is a very powerful tool for studying displacement cascades initiated by the neutrons when they interact with matter and thus evaluate the primary damage. The mean number of point defects created can be obtained with a fair standard error with a reasonable number of cascade simulations (10 to 20 [1]), however other cascades characteristics (spatial distribution, size and amount of defect clusters ...) display a huge variability. Therefore, they may need to be studied using faster methods such as the Binary Collision Approximation (BCA) which is several order of magnitude less time consuming. We have investigated the point defect distributions subsequent to atomic collision cascades by both MD (using EAM potentials for Fe) and its BCA. MD and its BCA lead to comparable point defect predictions. The significant similarities and differences are discussed.
Simulation of radiation damage in Fe alloys: an object kinetic Monte Carlo approach
Journal of Nuclear Materials, 2004
The reactor pressure vessel (RPV) steels used in current nuclear power plants embrittle as a consequence of the continuous irradiation with neutrons. Among other radiation effects, the experimentally observed formation of copper-rich defects is accepted to be one of the main causes of embrittlement. Therefore, an accurate description of the nucleation and growth under irradiation of these and other defects is fundamental for the prediction of the mechanical degradation that these materials undergo during operation, with a view to guarantee a safer plant life management. In this work we describe in detail the object kinetic Monte Carlo (OKMC) method that we developed, showing that it is well suited to investigate the evolution of radiation damage in simple Fe alloys (Fe, Fe-Cu) under irradiation conditions (temperature, dose and dose-rate) typical of experiments with different impinging particles and also operating conditions. The still open issue concerning the method is the determination of the mechanisms and parameters that should be introduced in the model in order to correctly reproduce the experimentally observed trends. The stateof-the-art, based on the input from atomistic simulation techniques, such as ab initio calculations, molecular dynamics (MD) and atomic kinetic Monte Carlo, is critically revised in detail and a sensitivity study on the effects of the choice of the reaction radii and the description of defect mobility is conducted. A few preliminary, but promising, results of favorable comparison with experimental observations are shown and possible further refinements of the model are briefly discussed.
Introducing chemistry in atomistic kinetic Monte Carlo simulations of Fe alloys under irradiation
physica status solidi (b), 2010
The evolution of alloy microstructures under non-equilibrium conditions such as irradiation is an important academic as wellindustrial issue. Atomistic kinetic Monte Carlo is one of the most versatile method which can be used to simulate the evolution of a complex microstructure at the atomic scale, dealing with elementary atomic mechanisms. It was developed more than 40 years ago to investigate diffusion events via the motion of a single vacancy, and the introduction of heterointerstitials or self-interstitials in the models is yet under development. This paper presents the key ingredients of the model, i.e. the algorithm, and some methods implemented to determine the cohesive energy as well as the activation energy. For purpose of simplicity and speed of calculations, most of the models developed so far apply to idealized lattices and model alloys, for example binary alloys. The extension of the models to more complex alloys is recent and an example of the simulation of multi-component Fe-CuNiMnSi alloys representative of pressure vessel steels is thus presented in more details. In particular, the adjustment procedures of the cohesive model are demonstrated as well as the validation of the model for vacancies and self-interstitials on thermal ageing and isochronal annealing experiments.
Journal of Nuclear Materials, 2006
Groups of displacement cascades calculated independently with different simulation models and computer codes are compared on a statistical basis. The parameters used for this comparison are the number of Frenkel pairs (FP) produced, the percentages of vacancies and self-interstitial atoms (SIAs) in clusters, the spatial extent and the aspect ratio of the vacancies and the SIAs formed in each cascade. One group of cascades was generated in the binary collision approximation (BCA) and all others by full molecular dynamics (MD). The MD results differ primarily due to the empirical interatomic potentials used and, to some extent, in code strategies. Cascades were generated in simulation boxes at different initial equilibrium temperatures. Only modest differences in the predicted numbers of FP are observed, but the other cascade parameters may differ by more than 100%. The consequences of these differences on long-term cluster growth in a radiation environment are examined by means of object kinetic Monte Carlo (OKMC) simulations. These were repeated with three different parameterizations of SIA and SIA cluster mobility. The differences encompassed low to high mobility, one-and three-dimensional migration of clusters, and complete immobility of large clusters. The OKMC evolution was followed until 0.1 dpa was reached. With the range of OKMC parameters used, cluster populations after 0.1 dpa differ by orders of magnitude. Using the groups of cascades from different sources induced no difference larger than a factor of 2 in the OKMC results. No correlation could be identified between the cascade parameters considered and the number densities of vacancies and SIAs predicted by OKMC to cluster in the long term. However, use of random point defect distributions instead of those obtained for displacement cascades as input for the OKMC modeling led to significantly different results.
Journal of Nuclear Materials, 2011
ABSTRACT Atomic displacement cascades in solids are complex phenomena, the outcome of which can be statistically characterised by properties such as their spatial extent, morphology and the spatial correlation of defects. Some properties scale in a simple way with parameters such as the cascade energy, others have limited variability with energy, for example point defect cluster size distributions. Taking advantage of the latter invariance, we use object kinetic Monte Carlo simulations to demonstrate that most properties of displacement cascade play no significant role in the evolution of point defect cluster size distributions after long enough time. It is suggested that reliable long-term predictions are possible, when using only the self-interstitial and vacancy cluster size distributions from low energy displacement cascades as building blocks to represent the complete spectrum of cascade energies obtained under neutron irradiation conditions. This is shown on the basis of recursive properties of displacement cascades evidenced for the first time and taking only approximately into account the average volumes in which vacancies and self-interstitial atoms are confined.The model has been successfully used to simulate the evolution of point defect clusters in iron for displacement rates in the range of 10−6 dpa/s and doses of the order of 0.1 dpa. The applicability beyond this range and to more complex materials is discussed.
The nature of high-energy radiation damage in iron: Modeling results
Understanding and predicting a material's performance in response to high-energy radiation damage, as well as designing future materials to be used in intense radiation environments, requires the knowledge of the structure, morphology and amount of radiation-induced structural changes 1-5 . We report the results of molecular dynamics simulations of high-energy radiation damage in iron in the range 0.2-0.5 MeV. We analyze and quantify the nature of collision cascades both at the global and local scale. We find that the structure of high-energy collision cascades becomes increasingly continuous as opposed to showing sub-cascade branching reported previously. At the local length scale, we find large defect clusters and novel small vacancy and interstitial clusters. These features form the basis for physical models aimed at understanding the effects of high energy radiation damage in structural materials.
The nature of high-energy radiation damage in iron
Journal of Physics: Condensed Matter, 2013
Understanding and predicting a material's performance in response to high-energy radiation damage, as well as designing future materials to be used in intense radiation environments, requires the knowledge of the structure, morphology and amount of radiation-induced structural changes 1-5. We report the results of molecular dynamics simulations of high-energy radiation damage in iron in the range 0.2-0.5 MeV. We analyze and quantify the nature of collision cascades both at the global and local scale. We find that the structure of high-energy collision cascades becomes increasingly continuous as opposed to showing sub-cascade branching reported previously. At the local length scale, we find large defect clusters and novel small vacancy and interstitial clusters. These features form the basis for physical models aimed at understanding the effects of high energy radiation damage in structural materials.