Effect of cascade overlap and C15 clusters on the damage evolution in Fe : An OKMC study

In order to investigate the long-term evolution of radiation-induced defects in the fission- and fusion-relevant material iron, we introduce cascade overlap effects into Object Kinetic Monte Carlo simulations. In addition to cascade overlap, we study the effect of introducing discrete C15 Laves phase clusters into the simulations. By applying either, none, or both of these effects we identify how they influence the evolution of the system. We find that both cascade overlap and C15 clusters affect the evolution of the radiation damage in different ways and on different time scales. Cascade overlap is found to reduce the number of Frenkel pairs. On the other hand, the explicit consideration of C15 Laves phase clusters increases the accumulation of defects at low dose. The results are compared to Molecular Dynamics simulation results under similar conditions.Peer reviewe

Modeling contact formation between atomic-sized gold tips via molecular dynamics

Quantum Matter and Optic

Object Kinetic Monte Carlo calculations of irradiated Fe-Cr dilute alloys: The effect of the interaction radius between substitutional Cr and self-interstitial Fe

ObjectKineticMonteCarlo models allow for the study of the evolution of the damage created by irradiation to time scales that are comparable to those achieved experimentally. Therefore, the essential ObjectKineticMonteCarlo parameters can be validated through comparison with experiments. However, this validation is not trivial since a large number of parameters is necessary, including migration energies of point defects and their clusters, binding energies of point defects in clusters, as well as the interactionradii. This is particularly cumbersome when describing an alloy, such as the Fe–Cr system, which is of interest for fusion energy applications. In this work we describe an ObjectKineticMonteCarlo model for Fe–Cr alloys in the dilute limit. The parameters used in the model come either from density functional theory calculations or from empirical interatomic potentials. This model is used to reproduce isochronal resistivity recovery experiments of electron irradiateddiluteFe–Cr alloys performed by Abe and Kuramoto. The comparison between the calculated results and the experiments reveal that an important parameter is the capture radius between substitutionalCr and self-interstitialFe atoms. A parametric study is presented on the effect of the capture radius on the simulated recovery curves

Multiscale modelling for fusion and fission materials: the M4F project

The M4F project brings together the fusion and fission materials communities working on the prediction of radiation damage production and evolution and its effects on the mechanical behaviour of irradiated ferritic/martensitic (F/M) steels. It is a multidisciplinary project in which several different experimental and computational materials science tools are integrated to understand and model the complex phenomena associated with the formation and evolution of irradiation induced defects and their effects on the macroscopic behaviour of the target materials. In particular the project focuses on two specific aspects: (1) To develop physical understanding and predictive models of the origin and consequences of localised deformation under irradiation in F/M steels; (2) To develop good practices and possibly advance towards the definition of protocols for the use of ion irradiation as a tool to evaluate radiation effects on materials. Nineteen modelling codes across different scales are being used and developed and an experimental validation programme based on the examination of materials irradiated with neutrons and ions is being carried out. The project enters now its 4th year and is close to delivering high-quality results. This paper overviews the work performed so far within the project, highlighting its impact for fission and fusion materials science.This work has received funding from the Euratom research and training programme 2014-2018 under grant agreement No. 755039 (M4F project)

Dose rate effects during damage accumulation in silicon

We combine molecular dynamics and Monte Carlo simulations to study damage accumulation and dose rate effects during irradiation of Silicon. We obtain the initial stage of the damage produced by heavy and light ions using classical molecular dynamics simulations. While heavy ions like As or Pt induce amorphization by single ion impact, light ions like B only produce point defects or small clusters of defects. The amorphous pockets generated by heavy ions are stable below room temperature and recrystallize at temperatures below the threshold for recrystallization of a planar amorphous-crystalline interface. The damage accumulation during light ion irradiation is simulated using a Monte Carlo model for defect diffusion. In this approach, we study the damage in the lattice as a function of dose and dose rate. A strong reduction in the total number of defects left in the lattice is observed for lower dose rates

Point defect production, geometry and stability in silicon: A molecular dynamics simulation study

We present results of molecular dynamics computer simulation studies of the threshold energy for point defect production in silicon. We employ computational cells with 8000 atoms at ambient temperature of 10 K that interact via the Stillinger-Weber potential. Our simulations address the orientation dependence of the defect production threshold as well as the structure and stability of the resulting vacancy-interstitial pairs. Near the directions, a vacancy tetrahedral-interstitial pair is produced for 25 eV recoils. However, at 30 eV recoil energy, the resulting interstitial is found to be the split dumbbell configuration. This Frenkel pair configuration is lower in energy than the former by 1.2 eV. Moreover, upon warming of the sample from 10 K the tetrahedral interstitial converts to a split before finally recombining with the vacancy. Along directions, a vacancy- split interstitial configuration is found at the threshold energy of 22 eV. Near directions, a wide variety of closed replacement chains are found to occur for recoil energies up to 45 eV. At 45 eV, the low energy vacancy- split configuration is found. At 300 K, the results are similar. We provide details on the atomic structure and relaxations near these defects as well as on their mobilities

Molecular dynamics studies of radiation effects in silicon carbide

We discuss results of molecular dynamics computer simulation studies of 3 keV and 5 keV displacement cascades in {beta}-SIC, and compare them to results of 5 keV cascades in pure silicon. The SiC simulations are performed with the Tersoff potential. For silicon we use the Stillinger-Weber potential. Simulations were carried out for Si recoils in 3 dimensional cubic computational cells With periodic boundary conditions and up to 175,616 atoms. The cascade lifetime in SiC is found to be extremely short. This, combined with the high melting temperature of SiC, precludes direct lattice amorphization during the cascade. Although large disordered regions result, these retain their basic crystalline structure. These results are in contrast with observations in pure silicon where direct-impact amorphization from the cascade is seen to take place. The SiC results also show anisotropy in the number of Si and C recoils as well as in the number of replacements in each sublattice. Details of the damage configurations obtained will be discussed