Crystal Structure and Phase Stability of Intermetallic Compounds

本计画的主要目的是在理论分析的基础上，预测与控制特定金属间化合物的晶体结构与微观结构。作为潜在的理论工具，我们采用了基于统计力学的分子轨道方法和集团变分方法的电子结构计算。前者用于构建“结构图”，其中指定了特定晶体结构的稳定区域。后者与从头算内能计算相结合，得到了一个合金体系的相图，其中出现了感兴趣的imc。这些理论上的努力反映在下面的实验说明中。各种合金元素被发现稳定的L12有序结构的Al 3 Ti imc，其特征在于在其二元状态下的D 022结构。在合金元素中，Cr和Mn对提高塑性最有效.在Ni-Al和Co-Al二元系的基础上，建立了三元系和四元系的相图，并在相图的多相区进行了力学性能改善的尝试。Ni_3Al-NiBe和Co_3 Ti-Ni_3Al是获得塑性的成功例子。

The main objectives of the present project are to predict and to control a crystal structure and a microstructure of a given intermetallic compound (imc) based on the sound theoretical analysis. As potential theoretical tools, we adopted the electronic structure calculation based on the molecular orbital method and Cluster Variation Method of statistical mechanics. The former was utilized to construct a "Structural Map" in which a stability region of a particular crystal structure is specified. The latter is combined with the ab initio internal energy calculation to obatain a phase diagram of an alloy system in which an imc of interest appears. These theoretical efforts are reflected in the folowing experimental achievments.1. Various alloying elements were found to stabilize the L12 ordered structure for the Al3Ti imc which is characterized by a D022 structure in its binary state. Among the alloying elements, it was confirmed that Cr and Mn were most effective in improving the ductility.2. The phase diagrams are established for ternary and quartery systems based on Ni-Al and Co-Al binary systems, and the improvement of mechanical properties was attempted in the multiphase region of the phase diagram. Ni3Al-NiBe and Co3Ti-Ni3Al are the succesful examples for which ductility is endowed.In addition, measurements of thermal conductivity are systematically performed for a series of intermetallic compound.