A Study on the Formation Process of Long Period Superlattice Structures in Alloys

60多年来，人们从理论和实验两个角度对金属合金的结构有序-无序转变进行了广泛的研究。通过X射线、中子和电子衍射测量，进行了一些开创性的实验工作。然而，有序-无序转变并不一定在样品的每个部分均匀进行，但它通常是非均匀现象，并通过形核和生长机制发展。因此，不仅要在倒易空间中进行微观观察，而且要在真实空间中进行微观观察。本工作利用透射电子显微镜研究了银镁合金中无序相形成长周期超晶格的过程。首次发现，有序和无序(或弱有序)区域在空间上周期性排列的亚稳态出现在有序化之前。费米面的嵌套被认为是这种有序的起源。

Structural order-disorder transition in metalic alloys have been investigated extensively for more than 60 years from both theoretical and experimental points of view. A number of pioneering experimental works have been performed by the x -ray, the neutron and the electron diffraction measurements. However, order-disorder transitions do not necessarily proceed homogeneously in every portion of the specimen, but it is usually heterogeneous phenomena and develops by the mechanism of nucleation and growth. Thus, it becomes important to do observation not only in reciprocal space but also in real space microscopically.In the present work, formation process of long period superlattice from disordered phase in Ag-Mg alloys has been studied by means of transmission electron microscopy. It was found for the first time that the ordering was preceded by a metastable state in which ordered and disordered (or weakly ordered) regions were periodically arranged spatially. The nesting of the fermi surface is proposed as the origin of this type of ordering.