Johnson Erik, Andersen Hans Henrik, Dahmen Ulrich
Nano Science Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
Microsc Res Tech. 2004 Aug;64(5-6):356-72. doi: 10.1002/jemt.20097.
Transmission electron microscopy has been used for structural and physical characterization of nanoscale inclusions of lead and noble gases in aluminum. When the inclusion sizes approach nanoscale dimensions, many of their properties are seen to deviate from similar properties in bulk and in most cases the deviations will increase as the inclusion sizes decrease. Binary alloys of lead and noble gases with aluminum are characterized by extremely low mutual solubilities and inclusions will, therefore, exist as practically pure components embedded in the aluminum matrix. Furthermore, the thermal vacancy mobility in aluminum at and above room temperature is sufficiently high to accommodate volume strains associated with the inclusions thus leading to virtually strain free crystals. The inclusions grow in parallel cube alignment with the aluminum matrix and have a cuboctahedral shape, which reflects directly the anisotropy of the interfacial energies. Inclusions in grain boundaries can have single crystalline or bicrystalline morphology that can be explained from a generalized Wulff analysis such as the xi-vector construction. The inclusions have been found to display a variety of nanoscale features such as high Laplace pressure, size-dependent superheating during melting, deviations from the Wulff shape displaying magic size effects, a shape dependence of edge energy, and so on. All these effects have been observed and monitored by TEM using conventional imaging conditions and high-resolution conditions in combination with in-situ analysis at elevated temperatures.
透射电子显微镜已被用于对铝中铅和稀有气体的纳米级夹杂物进行结构和物理表征。当夹杂物尺寸接近纳米级时，它们的许多性质会偏离其在体相中的类似性质，并且在大多数情况下，随着夹杂物尺寸减小，偏差会增大。铅和稀有气体与铝的二元合金具有极低的互溶性，因此夹杂物将以几乎纯的组分形式存在于嵌入铝基体中。此外，室温及以上温度下铝中的热空位迁移率足够高，足以适应与夹杂物相关的体积应变，从而形成几乎无应变的晶体。夹杂物与铝基体平行呈立方排列生长，呈立方八面体形状，这直接反映了界面能的各向异性。晶界中的夹杂物可以具有单晶或双晶形态，这可以通过广义的伍尔夫分析（如ξ矢量构造）来解释。已发现夹杂物呈现出各种纳米级特征，如高拉普拉斯压力、熔化过程中与尺寸相关的过热度、偏离伍尔夫形状显示出神奇尺寸效应、边缘能量的形状依赖性等等。所有这些效应都已通过透射电子显微镜在常规成像条件和高分辨率条件下，并结合高温原位分析进行了观察和监测。
