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

现代微电子和微机械设备包含微米级和亚微米级的金属元件。与较大的大块金属相比，这些部件的强度显着增加。描述它们独特性质的理论往往与描述经典大块金属部件强度的理论大不相同，尽管事实上这两种情况下金属是相同的。金属的塑性变形，在所有长度尺度上，都受到变形金属周围的外表面和内部表面状况的强烈影响。本研究将通过考虑各种类型的内外表面对变形过程的相对影响来探讨金属的长度依赖塑性变形问题。通过这种方式，对塑性变形过程的统一理解将会达到，这将极大地提高我们对现有的和新的金属部件的机械强度和延展性的预测能力，而不管它们的大小。***本研究将采用专门的微力学测试技术和数值模拟进行。单晶金样品，微米尺寸，将进行压缩测试，以评估外表面条件对其特征强度和塑性变形的影响。诸如晶体取向和外表面的物理约束等因素将被评估。双晶金和金合金样品也将进行压缩测试，以评估内表面状况对塑性变形过程的影响。这些表面的角取向偏差和物理约束等因素将被评估。恒定压缩载荷蠕变试验也将在上面列出的样品上进行，以评估内部和外部表面在阻碍随时间变化的塑性变形方面的作用。这些测试，以及测试前后对内外表面的广泛分析，将允许评估各种类型的表面对启动和维持塑性变形过程所需的临界应力和能量的影响。***这项研究将深刻地扩展我们对金属如何在所有长度尺度上塑性变形的理解，并将特别扩展我们对各种类型的内外表面对塑性变形过程的影响的理解。这些发现与所有金属系统相关，对于实现对现有金属部件（无论大小）强度的更好预测能力，以及开发具有微观结构特征（例如特定特征的内部和外部表面）的新部件，以产生最佳机械性能都是绝对必要的。

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.