Localized deformation and hardening in irradiated metals: Three-dimensional discrete dislocation dynamics simulations
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I. INTRODUCTION
WHEN fcc and bcc materials are subjected to irradiation with energetic particles (neutrons or protons), internal damage ensues. Damage accumulation (measurable defect density vs irradiation dose) saturates in fcc metals at defect densities of the order of 1024 m⫺3 for a variety of neutron irradiated metals near room temperature. One exception to this is palladium (Pd), where linear damage accumulation extends to higher total densities without any indication of saturation.[1] The damage is a result of collision cascades induced by the primary knock-on atom.[2] The study of damage microstructure reveals two types of material-dependent nanosize defect clusters: stacking-fault tetrahedras (SFTs) and Franksessile (FS) interstitial loops. For example, SFTs are the predominant defect type in Cu, which has a low stackingfault energy, whereas in high stacking-fault Pd, interstitial loops constitute the majority of observed defects.[1] The manner in which damage accumulates in a material has been extensively studied both experimentally using transmission electron microscopy (TEM) and computationally using molecular dynamics (MD) and kinetic MonteCarlo (kMC) simulations. Computer simulations have provided insight and explanation for experimental observations. For example, it was found that in bombarded Cu, large vacancy and interstitial clusters were produced within a few tens of picoseconds at the height of the cascade reaction.[3,4] TARIQ A. KHRAISHI, Assistant Professor, is with the Mechanical Engineering Department, University of New Mexico, Albuquerque, NM 87131. HUSSEIN M. ZBIB, Professor, is with the School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164. TOMAS DIAZ DE LA RUBIA, Deputy Division Leader of Science and Technology, Chemistry and Materials Science Directorate, is with Lawrence Livermore National Laboratory, Livermore, CA 94550. MAX VICTORIA, Adjoint Scientifique, is with the Ecole Polytechnique de Lausanne, CRPPFusion Technology Materials, 5232 Villigen PSI, Switzerland. Manuscript submitted April 3, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
Additionally, it was shown that vacancies can collapse to form SFTs, also within a few tens of picoseconds, in low stacking-fault metals at room temperature.[5] Based on MD results, it was suggested that interstitial clusters form glissile dislocation loops capable of migrating in one-dimension by thermal activation.[6] kMC simulations[7] of neutron irradiated Cu near room temperature show that over 90 pct of visible point-defect clusters are vacancy SFTs, which is in excellent agreement with experiments.[8,9] Finally, using computer simulations and experiment, de la Rubia et al.[10] presented a multiscale study of irradiation damage and subsequent alterations of mechanical properties. The microstructure of irradiation damage reveals two other features.[1] One represents a random homogeneous distribution of defects. The number density of defects is typically in the range of 1021 to 1024 m⫺3 depending on th
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