Effect of surfaces, internal and external, on the strength and ductility of metals

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Modern microelectronic and micromechanical devices contain tiny micrometer, and often submicrometer, size metal components. These components display significantly increased strength compared to their larger bulk metal counterparts. Theories describing their unique properties are often quite different than those describing the strength of classical bulk metal components despite the fact that the metal is the same in both cases. The plastic deformation of metals, across all length scales, is strongly influenced by the condition of the external surface around, and internal surfaces within, the deforming metal. This proposed study will approach the subject of length-scale dependent plastic deformation of metals by considering the relative influence of a variety of types of internal and external surfaces on the deformation process. In this way a unified understanding of the plastic deformation process will be arrived at that will greatly improve our predictive capability of the mechanical strength and ductility of existing, and new, metal components regardless of their size. *** This study will be undertaken by using specialized micromechanical testing techniques and numerical simulations. Monocrystalline gold samples, of micrometer size, will be tested in compression to assess the effect of external surface condition on their characteristic strength and plastic deformation. Factors such as crystallographic orientation and physical constraint of the external surfaces will be assessed. Bicrystalline gold and gold alloy samples will also be tested in compression to assess the effect of internal surface condition on the plastic deformation process. Factors such as angular misorientation and physical constraint of these surfaces will be assessed. Constant compressive load creep tests will also be performed on samples listed above to assess the role of the internal and external surfaces on impeding time-dependent plastic deformation. These tests, along with extensive analysis of the internal and external surfaces before and after testing, will allow assessment to be made of the effect of the various types of surfaces on the critical stress and energy necessary to initiate, and sustain, the plastic deformation process. *** This research will profoundly expand our understanding of how metals deform plastically across all length scales and will specifically expand our understanding of the effect of various types of internal and external surfaces on the plastic deformation process. These findings are relevant to all metal systems and are absolutely necessary for achieving better predictive capabilities of the strength of existing metal components, large and small, and for developing new components with microstructural features, such as internal and external surfaces of specific characteristics, that are tailored to produce optimal mechanical performance.