Division of Engineering and Applied Sciences, California Institute of Technology, 1200 E. California Blvd, MC 309-81, Pasadena, California 91125, USA.
Nat Nanotechnol. 2012 Sep;7(9):594-601. doi: 10.1038/nnano.2012.116. Epub 2012 Jul 15.
Nanotwinned metals are attractive in many applications because they simultaneously demonstrate high strength and high ductility, characteristics that are usually thought to be mutually exclusive. However, most nanotwinned metals are produced in polycrystalline forms and therefore contain randomly oriented twin and grain boundaries making it difficult to determine the origins of their useful mechanical properties. Here, we report the fabrication of arrays of vertically aligned copper nanopillars that contain a very high density of periodic twin boundaries and no grain boundaries or other microstructural features. We use tension experiments, transmission electron microscopy and atomistic simulations to investigate the influence of diameter, twin-boundary spacing and twin-boundary orientation on the mechanical responses of individual nanopillars. We observe a brittle-to-ductile transition in samples with orthogonally oriented twin boundaries as the twin-boundary spacing decreases below a critical value (∼3-4 nm for copper). We also find that nanopillars with slanted twin boundaries deform via shear offsets and significant detwinning. The ability to decouple nanotwins from other microstructural features should lead to an improved understanding of the mechanical properties of nanotwinned metals.
纳米孪晶金属在许多应用中很有吸引力，因为它们同时具有高强度和高延展性，而这两个特性通常被认为是相互排斥的。然而，大多数纳米孪晶金属都是多晶形式的，因此含有随机取向的孪晶界和晶界，这使得很难确定它们有用的机械性能的起源。在这里，我们报告了垂直排列的铜纳米柱阵列的制造，这些纳米柱含有非常高密度的周期性孪晶界，没有晶界或其他微观结构特征。我们使用拉伸实验、透射电子显微镜和原子模拟来研究直径、孪晶界间距和孪晶界取向对单个纳米柱机械响应的影响。我们观察到具有正交孪晶界的样品在孪晶界间距低于临界值（对于铜约为 3-4nm）时发生从脆性到延性的转变。我们还发现，具有倾斜孪晶界的纳米柱通过剪切偏移和显著的退孪晶变形。将纳米孪晶与其他微观结构特征分离的能力应该有助于更好地理解纳米孪晶金属的机械性能。
