Length-scale Effects in Cascade Damage Production in Iron
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1125-R05-05
Length-scale Effects in Cascade Damage Production in Iron R. E. Stoller1, P. J. Kamenski2, and Yu. N. Osetsky1 1
Materials Science and Technology Division Oak Ridge National Laboratory, Oak Ridge, TN 37831-6138 2
Department of Materials Science and Engineering University of Wisconsin, Madison, WI (now University of Oxford, UK) Abstract
Molecular dynamics simulations provide an atomistic description of the processes that control primary radiation damage formation in atomic displacement cascades. An extensive database of simulations describing cascade damage production in single crystal iron has been compiled using a modified version of the interatomic potential developed by Finnis and Sinclair. This same potential has been used to investigate primary damage formation in nanocrystalline iron in order to have a direct comparison with the single crystal results. A statistically significant number of simulations were carried out at cascade energies of 10 keV and 20 keV and temperatures of 100 and 600K to make this comparison. The results demonstrate a significant influence of nearby grain boundaries as a sink for mobile defects during the cascade cooling phase. This alters the residual primary damage that survives the cascade event. Compared to single crystal, substantially fewer interstitials survive in the nanograined iron, while the number of surviving vacancies is similar or slightly greater than the single crystal result. The fraction of the surviving interstitials contained in clusters is also reduced. The asymmetry in the survival of the two types of point defects is likely to alter damage accumulation at longer times. Introduction Primary damage formation in irradiated metals due to atomic displacement cascades has been extensively investigated using the method of molecular dynamics (MD) [1-11]. These MD simulations have led to a well-accepted understanding of the underlying processes that lead to the formation of stable (on MD time scales) distributions of point defects, i.e. vacancies and interstitials. Both types of point defects are found in the form of isolated mono-defects as well as small defect clusters. The influence of variables such as cascade (or primary knock-on atom, PKA) energy and irradiation temperature have been determined [8] and differences due to the choice of interatomic potential have been explored [10]. A particularly large database of simulations has been accumulated for iron [9] using a modified version of the interatomic potential developed by Finnis and Sinclair [3,12 ]. Like most MD studies of displacement cascades, the simulations in this database were carried out using perfect crystals with periodic boundary conditions. To the extent that the simulations are representative of radiation damage in iron, they represent only the behavior of single crystal materials.
There has been a limited amount of research carried out to investigate the potential influence of grain size on primary damage formation [11, 13-16]. Computational limitations dictate that such work would f
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