Study of grain-boundary-dislocation interactions by advanced in situ µLaue diffraction

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The enormous influence of grain boundaries on the plastic deformation behavior of engineering materials has been known for several decades and is of paramount concern for industrial applications worldwide. Nevertheless, up to now no thorough understanding of the interaction processes of single dislocations with different types of grain boundaries exist. Macroscopically these effects are often smeared out due to the infinite number of available dislocation sources and grain-boundaries present in engineering materials. However, in micron sized samples, where the number and size of dislocation sources are limited, few dislocations control the plastic deformation of the entire device. This size effect was intensively studied over the last decade in single crystalline materials and a basic understanding for face-centered-cubic (FCC) materials exists. However, for material structures containing only a few grain-boundaries a thorough understanding is lacking.A size effect of mechanical properties was recently also reported for micron sized bi-crystals. Due to the limited number of dislocation sources, the higher stresses and the shorter diffusion path it is well possible, that the grain-boundary-dislocation interaction processes change at the micron scale. Controlling the grain-boundary parameters and the loading direction allows for an activation of macroscopically unfavored or unidentifiable interaction processes. Thus, bi-crystalline micro compression samples allow for studying grain-boundary-dislocation interaction processes in general, but particularly their size dependency.In the proposed work the mechanical behavior of bi-crystalline, micron sized copper (Cu) samples should be analyzed by advanced diffraction and imaging methods. As a modell system, micromechanical samples containing different grain and twin boundaries will be prepared by focused ion beam milling (FIB) and subsequently tested at the micro Laue endstation of the CRG-IF at BM32 of the ESRF synchrotron source. Main focus of the work is the continuous measurement of distribution and density of geometrical necessary dislocations (GNDs) and elastic strains during the deformation of micron sized pillars by in situ micro Laue (µLaue) diffraction. These data will be correlated to the mechanical data (strength, hardening) globally measured during the experiment. The microLaue experiments will be supported by complementary state of the art methods like transmission electron microscopy (TEM), molecular dynamics (MD) and discrete dislocation dynamics (DDD) simulations. We aim for the understanding of size-dependent bi-crystalline plasticity as well as the quantification and understanding of involved grain-boundary dislocation interaction processes.