Dislocation Behavior During Deformation- Combining Experiments, Simulation and Modeling.
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DISLOCATION BEHAVIOR DURING DEFORMATION- COMBINING EXPERIMENTS, SIMULATION AND MODELING. I.M. Robertson and J. Robach, Dept. of Mater. Sc. and Engin., Univ. of Illinois, Urbana, IL; B. Wirth and A. Arsenlis, Lawrence Livermore National laboratory, Livermore, CA. ABSTRACT In situ straining in the transmission electron microscope has been combined with molecular dynamics computer simulations to investigate the nature of the interaction of glissile dislocations with radiation-produced defects (loops, stacking-fault tetrahedra, and He bubbles), and to determine the mechanisms by which the dislocation loops and stacking-fault tetrahedra are annihilated and defect-free channels are created. The defect pinning strength depends on the defect and on the interaction geometry. The experiments and simulations show that a single interaction is not always sufficient to annihilate a dislocation loop or a stacking-fault tetrahedra and that the nature of the defect may be changed because of the interaction. The edge/screw character of the dislocation is also important as they have different efficiencies for annihilating a defect. The dislocations responsible for creating the defect-free channels are not the preexisting dislocations but originate from grain boundaries and other stress concentrators. Cross-slip of dislocations within the channels is important for clearing and widening the channel and can create new channels. Based on these observations a dispersed-barrier hardening model in which the influence of the radiation defects and dislocation density are combined. The resulting model predicts the observed behavior, including the apparent yield drop at high defect densities. INTRODUCTION Dislocations and their interactions with other microstructural features, such as impurity atoms, precipitates, dispersoids, dislocations, and grain boundaries determine the mechanical properties of metallic systems. However, despite considerable progress, no clear methodology exists for transferring this information into a predictive macroscopic constitutive relationship. These relationships are needed to assess the response and reliability of materials exposed to extreme conditions (temperature, stress, and pressure), especially for situations in which experimental testing is impractical or impossible, and to decrease the time to bring new materials into technological applications. The ideal model should incorporate the behavior at different length and time scales within one grand multiscale scheme. Such a scheme is, however, impractical and lower length scale models are used to provide fundamental information to serve as the foundation for the next higher length scale. Some features included in the models have necessarily been phenomenological or representative and adopted to improve computational efficiency rather than represent physical realism. As requirements of models become more stringent, it has become increasingly necessary to determine which interactions and mechanisms need to be included in all models.
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