Multiscale Modeling of Helium-Vacancy Cluster Nucleation under Irradiation: A Kinetic Monte-Carlo Approach
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1215-V05-07
Multiscale Modeling of Helium-Vacancy Cluster Nucleation under Irradiation: a Kinetic Monte-Carlo Approach. Tomoaki Suzudo1 Masatake Yamaguchi1, Hideo Kabraki1 and Ken-ichi Ebihara1 1 Center for Computational Science and e-Systems, Japan Atomic Energy Agency, Tokai-mura, 319-1195, Japan
ABSTRACT We applied ab initio calculation and an object kinetic Monte Carlo modeling to the study of He-vacancy cluster nucleation under irradiation in bcc and fcc Fe, which are surrogate materials for ferritic/martensitic and austenitic steels, respectively. The ab initio calculations provided parameters for the object kinetic Monte Carlo model, such as the migration energies of point defects and the dissociation energies of He and vacancy to He-vacancy clusters. We specially focused on the simulation of high He/dpa irradiation such as He-implantation into the materials and tracked the nucleation of clusters and the fate of point defects such as SIAs, vacancies, and He atoms. We found no major difference of He-vacancy cluster nucleation between bcc and fcc Fe when we ignore the intracascade clustering even if the migration energies of point defects are significantly different between the two crystals. INTRODUCTION He produced in steel by high-energy neutron radiation causes significant change in its mechanical properties, see e.g. [1] and references therein. The swelling caused by the nucleation and growth of He bubbles is a primary concern. Both of ferritic/martensitic and austenitic steels are considered as candidate structural materials of fast breeder reactors, and the swelling behavior of these steels are comparatively discussed [2, 3]. Many experimental evidences show that ferritic/martensitic steels are generally more swelling-resistant than austenitic steels [2]. This difference is numerically studied by molecular dynamics, and the defect configurations after a radiation cascade in bcc Fe and fcc Cu reveals that intracascade vacancy clusters in fcc Cu are larger than those produced in bcc Fe [4]. This result is considered as a cause of swelling vulnerability of fcc metals [5]. However, the other factors influencing the swelling behaviors, such as point-defect migrations and point-defect dissociation from clusters, have not been thoroughly examined yet. In the present paper, we modeled He-vacancy clustering and conducted comparative studies between bcc and fcc Fe, which are surrogate materials for ferritic/martensitic and austenitic steels, respectively. Using ab initio methodology, we calculated the migration energies of point defects and He and vacancy binding energies to He-vacancy clusters, all of which are key parameters for the nucleation and growth of He-vacancy clusters. Then we conducted object kinetic Monte Carlo simulations using the parameters obtained by the ab initio calculations. The main aim of this paper is to compare He-vacancy clustering behavior between bcc and fcc Fe under irradiation.
AB INITIO CALCULATIONS We derived ab initio energies related to the nucleation of He-vacancy clusters und
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