Atomic Configuration in Bainite of a Cu₄₅Zn₄₀Au₁₅ Alloy Examined by ALCHEMI

¹ The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihoga-oka, Ibaraki, Osaka 567, Japan
² Government Industrial Research, Nagoya, 1-1 Hirate-cho, Kitaku, Nagoya, Aichi 462, Japan
³ Department of Materials Science and Engineering, Kanazawa Institute of Technology, Nonoichi, Ishikawa 921, Japan

Abstract

The atomic configuration in the bainite of a Сu₄₅Zn₄₀Au₁₅ alloy with a L2₁ type ordered structure in parent phase has been studied by means of ALCHEMI. Thin bainite plates which are supposed to be at early stages of formation possess the 18R type structure like the martensite of the same alloy system formed at subzero temperature. As far as electron diffraction is concerned, it appears that they inherit the ordered configuration of atoms in the parent phase completely. However, when closely examined by ALCHEMI, the atomic configuration is found to differ slightly from that in the parent phase. A part of Cu and Zn atoms in the bainite interchange their sites with each other, which are in the first nearest neighbor relation in the parent phase. This type of disordering is different from that recently observed in the martensite formed at subzero temperature and subsequently aged sufficiently at room temperature. These facts suggest that the bainite is not the martensite subjected to aging at temperature alter its formation.