Rate theory modeling of defect evolution under cascade damage conditions: the influence of vacancy-type cascade remnants on defect evolution (original) (raw)
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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.
Journal of Nuclear Materials, 2006
The existence of an interplay between the structure of displacement cascades and point defect mobility that influences the long-term evolution of primary damage in a-Fe is revealed by applying an object kinetic Monte Carlo (OKMC) method. The investigation was carried out using different parameter sets, which primarily differ in the description of self-interstitial atom (SIA) cluster mobility. Two sets of molecular dynamics cascades (produced with the DYMOKA and the MOLDY codes, using different interatomic potentials) and one set of cascades produced in the binary collision approximation with the MARLOWE code, using a Ziegler-Biersack-Littmark (ZBL) potential were separately used as input for radiation damage simulation. The point defect cluster populations obtained after reaching 0.1 dpa were analyzed in each case and compared. It turns out that the relative influence of using different input cascade datasets on the damage features that evolve depends on which OKMC parameter set is employed. Published by Elsevier B.V.
Classical nucleation theory of microstructure development under cascade-damage irradiation
Journal of Nuclear Materials, 2003
Cascade irradiation produces a significant fraction of the damage in the form of small mobile and immobile vacancy and interstitial clusters. This has led to the introduction of the Woo-Singh production bias theory. In the pursuant studies, the predominant effort that has been spent is in investigating the validity of the concept, and in its usefulness in complementing the traditional theory based on the concept of sink bias. Although plenty of theoretical and experimental results supports the concept, relatively little attention has been paid to the important area of microstructure nucleation. Within the framework of the classical theory of nucleation of overcritical precipitates from small subcritical nuclei, the nucleation processes at elevated temperatures of both voids and interstitial loops from the primary clusters are similar, and can be similarly treated. Recognizing the importance of stochastic fluctuations in the evolution of small embryos, a single-component nucleation theory is formulated using the Fokker-Planck equation, to take into account the stochastic effects of the fluxes of mobile defects, arising from the random nature of diffusion jumps and cascade initiation. Analytic solutions for the separate cases of voids and Frank loops are obtained, and the corresponding effects on the evolution of the microstructure are discussed.
Defect accumulation under cascade damage conditions
Journal of Nuclear Materials, 1994
There is now ample evidence from both experimental and computer simulation studies that in displacement cascades not only intense recombination takes place but also efficient clustering of both self-interstitial atoms (SIAs) and vacancies. The size distributions of the two types of defects produced in cascades are not only different but this difference is also temperature dependent because of the different thermal stabilities of SIA and vacancy clusters. This asymmetry in the production of SIAs and vacancies has been termed "production bias". In the present paper, the basic physics of the defect reactions kinetics associated with the specific features of cascade damage is described, with emphasis on asymmetries between SIA and vacancy type defects concerning their production, stability, mobilif and interactions with other defects. Defect accumulation under cascade damage conditions is discussed in terms of this reaction kinetics taking into account cluster production, dissociation, migration and annihilation at extended sinks. Microstructural features which are characteristic of cascade damage and cannot be explained in terms of the conventional single defect reaction kinetics are emphasized, in particular the heterogeneous microstructural evolution at low doses and the dose and temperature dependence of swelling.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005
Displacement cascades obtained by full molecular dynamics and in its binary collision approximation, as well as random point defect distributions, all having similar overall morphologies, are used as input for long-term radiation damage simulation by an object kinetic Monte Carlo method in a-iron. This model treats naturally point defect fluxes on cascades regions, resulting from cascades generated in other regions, in a realistic way. This study shows the significant effect of the internal structure of displacement cascades and, in particular, SIA agglomeration on the long-term evolution of defect cluster growth under irradiation.
Aspects of microstructure evolution under cascade damage conditions
Journal of Nuclear Materials, 1997
The conventional theoretical models describing the damage accumulation, particularly void swelling, under cascade damage conditions do not include treatments of important features such as intracascade clustering of self-interstitial atoms (SIAs) and one-dimensional glide of SIA clusters produced in the cascades. Recently, it has been suggested that the problem can be treated in terms of 'production bias' and one-dimensional glide of small SIA clusters. In the earlier treatments a 'mean size approximation' was used for the defect clusters and cavities evolving during irradiation. In the present work, we use the 'size distribution function' to determine the dose dependence of sink strengths, vacancy supersaturation and void swelling as a function of dislocation density and grain size within the framework of production bias model and glide of small SIA clusters. In this work, the role of the sessile-glissile loop transformation (due to vacancy supersaturation) on the damage accumulation behaviour is included. The calculated results on void swelling are compared with the experimental results as well as the results of the earlier calculations using the 'mean size approximation'. The calculated results agree very well with the experimental results. 0 1997 Elsevier Science B.V.
2006
The multiscale modeling scheme encompasses models from the atomistic to the continuum scale. Phenomena at the mesoscale are typically simulated using reaction rate theory (RT), Monte Carlo (MC), or phase field models. These mesoscale models are appropriate for application to problems that involve intermediate length scales (µm to >mm), and timescales from diffusion (~µs) to long-term microstructural evolution (~years). Phenomena at this scale have the most direct impact on mechanical properties in structural materials of interest to nuclear energy systems, and are also the most accessible to direct comparison between the results of simulations and experiments. Recent advances in computational power have substantially expanded the range of application for MC models. Although the RT and MC models can be used simulate the same phenomena, many of the details are handled quite differently in the two approaches. A direct comparison of the RT and MC descriptions has been made in the domain of point defect cluster dynamics modeling, which is relevant to both the nucleation and evolution of radiation-induced defect structures. The relative merits and limitations of the two approaches are discussed, and the predictions of the two approaches are compared for specific irradiation conditions.
Fluctuations of point-defect fluxes to sinks under cascade damage irradiation
Journal of Nuclear Materials, 1996
The arrival rates of point defects at sinks are not deterministic, but probabilistic and fluctuate with time because of the random nature of diffusing jumps and cascade occurrence. The influence of such fluctuations on the evolution of different sink types is analyzed, and discussed in comparison with literature. The 'diffusion coefficients' of the size-distribution function for several sink types (voids, interstitial and vacancy loops and clusters) are derived from first principles. The "diffusion coefficient' for the fluctuations of the climb rate of network dislocations is also calculated. The application of the present formalism to the evolution of the primary clusters of point defects generated during cascade damage is also discussed.
Journal of Nuclear Materials, 1994
Using a composite model of point defect behavior and microstructural evolution, the influence of cascade vacancy cluster formation and vacancy trapping at solute atoms on the point defect fluxes, point defect clustering and extended defect development was investigated. The point defect model calculates the concentrations of isolated and trapped point defects, and of simple or complex clusters. The extended defect model consists of individual rate theory models describing the evolution of cavities, Frank loops and network dislocations. Cascade vacancy clusters were observed to become the dominant sink for point defects in the early stages of irradiation at low to intermediate temperature. Therefore, the sink strength of the vacancy clusters largely determines the point defect flux and agglomeration rates. The calculations also showed that solute traps affect the irradiated microstructure to a large extent for certain combinations of trap concentration and trapping energy. Both the trap concentration and trapping energy have a non-monotonic effect on vacancy clustering though they do not change the interstitial flux significantly.