Crystal Structure and Phase Stability of Intermetallic Compounds

点击翻译按钮获取中文摘要

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.