Elemental distribution at diffusion bonding interface of FeAlSi thermoelectric material and Cu

Abstract Thermoelectric generation is a promising technology for the realization of a carbon–neutral society. Many kinds of semiconductors are developed as high-efficiency thermoelectric materials. For example, some types of silicide semiconductors consisting of widely available low-cost elements are known to be promising materials. Among them, FeAlSi thermoelectric (FAST) material is a newly developed derivative of iron-silicide material that consists of commonly available non-toxic elements. This material has an excellent Seebeck coefficient up to temperatures of 500 K. With thermoelectric device fabrication, soldering is mainly used to connect FAST material and metal electrodes. However, this connection is unstable in a medium temperature range because the solder melts. Therefore, we investigated the diffusion bonding of FAST material and copper plate, which is stable in a medium temperature range. In this study, we determine the bonding temperature range that allows successful bonding. Furthermore, the elemental distribution at the bonding interface was investigated using EPMA. The mutual diffusion of Al and Cu is dominant in the diffusion bonding process. Furthermore, the crystalline phases of the bonded joint area are investigated using X-ray diffraction. The spectra show that the Fe-Si and Cu-Al phases were precipitated in the Cu-diffused area of the FAST material. These results show that the mutual diffusion and eutectoid reaction of Cu and Al contribute to the diffusion bonding process.