A Study of Micro Structure in Bonded Layer (Part 1)

Abstract

As a basic study of brazing, two dissimilar metals in contact with each other were heated to a specified temperature and fused in an electric furnace, then the micrographic structure of the bonded layer was studied to establish the relation between the microstructure of the layer and the heating temperature.
As the simplest case, this paper is concerned with the microstructure of the combination of pure metals which form eutectics. The microstructure of bonded layer was determined by X-ray microanalyser and X-ray diffractometer.
Six combinations (Bi-Cd, Bi-Sn, Ti-Cu, Ti-Co, Ti-Ni and Zr-Ni) were treated as the specimen, each combination being examined individually. The following results were obtained:
i) The temperature for producing the molten layer must be, at least, over the lowest (or the first) eutectic temperature on the equilibrium diagram, and the composition of the molten layer agrees with that of eutectic point (see photo. 1, 4, 8, 13).
ii) When the temperature rises further and attains the upper (or second) eutectic point for instance a eutectic temperature, 1135°C, 82 wt% Co system such as the case of Ti-CO system, in the case of Ti-Cu and Zr-Ni, the second eutectic structure co-exists with the first eutectic structure depending on the speed of its producing process (see photo. 6, 14). However, in the case of Ti-Co and Ti-Ni, the whole specimen melts by heat which is produced by metallic compound formation constituting its eutectic structure (see photo. 9, 11).