Shapes and sizes of nanoscale Pb inclusions in Al
Shapes and sizes of nanoscale Pb inclusions in Al
复制标题
Al 中纳米级 Pb 夹杂物的形状和尺寸
DOI：
10.1016/s0921-5093(00)01462-3
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发表时间：
2001
期刊：
影响因子：
6.4
通讯作者：
T. Fujii
中科院分区：
文献类型：
--
作者：
E. Johnson;A. Johansen;U. Dahmen;S. Chen;T. Fujii
Al-Pb合金是一晶合金，其特点是液相区有较大的混相间隙，固相区相互溶解度极有限。由于混相间隙的存在，使得合金在常规工艺中难以制备。然而，通过快速凝固、离子注入、球磨和物理气相沉积等亚稳工艺可以制备出Al基体中细小Pb夹杂物相对均匀的合金。前两种技术已被用于制造0.5-3at的铝合金。% Pb。合金中含有纳米级Pb夹杂体，离子注入后尺寸在1 ~ 20nm之间，快速凝固后尺寸在10 ~ 500nm之间。嵌入Al基体中的夹杂物为单晶，它们与基体呈平行的立方体排列。它们具有立方体形状，具有原子光滑的{111}和{100}面，这是由界面能量的最小化决定的。利用高分辨率透射电镜，研究了两种偏离经典伍尔夫结构而改变包裹体形状的偏差。最小的夹杂物尺寸小于20nm左右，采用一系列与残余应变能出现周期性极小值有关的神奇尺寸。同样，在此尺寸范围内，立方体边缘的能量贡献变得不可忽略，导致包裹体的纵横比随着尺寸的减小而增加。位于晶界的夹杂物一般为单晶形态，其中一部分呈面状，与基体晶粒平行呈立方体排列，另一部分呈近似球形帽状。在孪晶界和{111}捻度界等特殊情况下，夹杂物为双晶，各部分与各自的晶粒排列，两部分被类似于基体的边界隔开。这些形状可以用Cahn-Hoffman ξ向量构造来解释，它推广了Wulff构造来确定各向异性界面及其连接处的平衡形状。
Al–Pb alloys are monotectic and characterized by a large miscibility gap in the liquid phase area and extremely limited mutual solubility in the solid phase. Due to the extent of the miscibility gap the alloys are difficult to make in conventional processing. However, alloys with relatively homogeneous microstructures of fine Pb inclusions in an Al matrix can be made by metastable processing such as rapid solidification, ion implantation, ball milling and physical vapor deposition. The first two techniques have been employed to make alloys of Al with 0.5–3at.% Pb. The alloys contain fine dispersions of nanoscale Pb inclusions with sizes in the range from 1 to about 20nm after ion implantation and from about 10–500nm after rapid solidification. Inclusions embedded in the Al matrix are single crystalline, and they grow in parallel cube alignment with the matrix. They have cuboctahedral shape with atomically smooth {111} and {100} facets determined from a minimization of the interface energy. Using high resolution TEM, two types of deviations from the classical Wulff construction which alter the shape of the inclusions, have been studied. The smallest inclusions, less than about 20nm in size, adopt a series of magic sizes that can be related to the occurrence of periodic minima in the residual strain energy. Likewise, in this size range, the energy contribution from the cuboctahedral edges becomes non-negligible leading to an increase in the aspect ratio of the inclusions with decreasing size. Inclusions located in grain boundaries in general adopt a single crystal morphology where one part is faceted and grows in parallel cube alignment with the matrix grain, while the other part has a shape approximating a spherical cap. In special cases such as twin boundaries and {111} twist boundaries, the inclusions are bicrystalline where each part is aligned with the respective grain and the two parts are separated by a boundary similar to that of the matrix. These shapes can be explained using the Cahn–Hoffman ξ-vector construction, which generalizes the Wulff construction to determine equilibrium shapes at anisotropic interfaces and their junctions.