Modeling Cascade Aging in Dilute Fe-Cu Alloys
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Modeling Cascade Aging in Dilute Fe-Cu Alloys B. D. Wirth1 and G. R. Odette2 1 Lawrence Livermore National Laboratory, Livermore, CA 94551 2 University of California, Santa Barbara, Santa Barbara, CA 93106 ABSTRACT The continued safe operation of nuclear reactors and their potential for lifetime extension depends on ensuring reactor pressure vessel integrity. Reactor pressure vessels and structural materials used in nuclear energy applications are exposed to intense neutron fields that create highly non-equilibrium defect concentrations, consisting of a shell of self-interstitial atom and clusters surrounding a vacancy-rich core, over picosecond time scales. This spatially correlated defect production initiates a long chain of events responsible for microstructure evolution and hence irradiation embrittlement. In this paper, we describe the combined use of molecular dynamics (MD) and kinetic lattice Monte Carlo (KMC) to simulate the long-term rearrangement (aging) of displacement cascades in dilute Fe-Cu alloys. The simulations reveal the formation of a continuous distribution of three dimensional cascade vacancy-Cu cluster complexes and demonstrate the critical importance of spatial, as well as short and long-time correlated processes that mediate the effective production of primary defects. Finally, this approach can generate production cross-sections for vacancy-Cu clusters that can then be used in rate theory type models of long term global micro and microstructural evolution. INTRODUCTION Radiation damage, and its attendant consequence to a wide spectrum of material properties, is a central issue in many advanced technologies, ranging from ion beam processing to the development of fusion power [1]. The fundamental objective of radiation effects modeling is predicting the generation, transport, fate and consequences of all defect species created by irradiation. Modeling radiation effects presents many challenges. Pertinent processes encompass the atomic nucleus all the way to structural component length scales, spanning more than 15 orders of magnitude. Time scales span more than 24 orders of magnitude, with the shortest being less than a femtosecond. Further, radiation effects involve the interaction of a multitude of physical processes, which are briefly described in the next section. This emphasizes the importance of closely integrating models with experiment, including detailed microstructural characterization studies. Radiation damage begins with the creation of energetic (typically a few tens of keV) primary recoil atoms (PRA) in high-energy neutron-nuclear interactions. The resulting displacement cascades initially develop and cool over picosecond time scales, resulting in a shell of self-interstitial atom (SIA) and SIA clusters, surrounding a vacancy-rich core [2-5]. This spatially correlated defect production initiates a long chain of events in reactor pressure vessel (RPV) steels responsible for microstructure evolution, and hence to irradiation embrittlement. In the case of embrittlement of RPV steels
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