It is now possible to create perfect crystal nanowires of many metals. The deformation of such objects requires a good understanding of the processes involved in plasticity at the nanoscale. Isotropic compression of such nanometre scale micropillars is a good model system to understand the plasticity. Here we investigate these phenomena using Molecular Dynamics (MD) simulations of nanometre scale single crystal BCC iron pillars in compression.
We find that pillars with large length to width ratio may buckle under high strain rates. The type of buckling behaviour depends sensitively on the boundary conditions used: periodic boundary conditions allow for rotation at top and bottom of the pillar, and result in an S shaped buckle, by contrast fixed boundaries enforce a C shape. Pillars with a length to width ratio closer to that used in experimental micropillar compression studies show deformation behaviour dominated by slip, in agreement with the experiments. For micropillars oriented along <100>, slip occurs on <110> planes and localized slip bands are formed. Pillars of this size experience higher stresses than bulk materials before yielding takes place. One might expect that this may be in part due to the lack of nucleation sites needed to induce slip. However, further simulations with possible dislocation sources: a shorter iron pillar containing a spherical grain boundary, and a similar pillar containing jagged edges did not show a decreased yield strength.
Defect-controlled twin activation in crystallographically equivalent magnesium micropillars
RWTH Aachen University（亚琛工业大学）；CNRS, Université de Lorraine, Arts et Métiers Institute of Technology（法国国家科学研究中心，洛林大学，国立工艺学院）；Helmholtz Zentrum Hereon（海姆霍兹HEREON中心）
Low-temperature nanoscale heat transport in a gadolinium iron garnet heterostructure probed by ultrafast x-ray diffraction
利用时间分辨X射线衍射技术研究了Pt/Gd 3Fe 5 O 12//Gd 3Ga 5 O 12金属/氧化物异质结的低温热输运性质。脉冲飞秒光信号在Pt层中产生快速的温度上升，随后热传输到Gd 3Fe 5 O 12（GdIG）薄膜和Gd 3Ga 5 O 12（GGG）衬底中。使用基于加速器的飞秒X射线源跟踪来自GdIG层的X射线衍射的时间依赖性。超快衍射测量探测GdIG（1 - 1 2）X射线反射在掠入射X射线衍射几何结构中的强度。的衍射X射线强度的变化与模型，包括热传输和GdIG晶格参数的温度依赖性的比较允许的Pt/GdIG和GdIG//GGG接口的热导率被确定。GdIG层的低温热膨胀性质的互补同步加速器X射线衍射研究提供了GdIG晶格参数的温度依赖性的精确校准。从时间分辨衍射研究确定的Pt/GdIG和GdIG//GGG接口的界面热导是相同的数量级的金属/氧化物和外延介电界面的先前报告。Pt/GdIG//GGG异质结构的热参数将有助于热传输器件和纳米结构的设计和实现。
