As a basic study of brazing, the relation between the micrographic structure of bonded layer and the heating temperature was established for metal combination of Ag-Sn, Cu-Zn, etc., near soft soldering; and action of phases was studied. The microstructure of bonded layer was determined by X-ray microanalyses, etc.
The following results were obtained:
1) In combinations having equillibrium diagrams of peritectic reaction, according to the rising temperature, the first phase appeared at bonded layer which was the intermetallic compound of the highest concentration of low melting metal (e.g. γ phase of Ag-Sri, η phase of Cu-Sn). The other phases may be formed extremely near the bonded layer, but they were not observed by the microscope. The phases of extremely large solid diffusion were formed at comparatively low temperature adjoining the above-mentioned phases.
2) Ni-rich solid solution of Ni-Sn appeared after intermetallic compounds of low melting temperature. Other combinations were similar.
3) β phase of Ni-Sn and ε phase of Cu-Sn were formed by solid diffusion at 920°C, 302°C which were lower than melting temperature of these phases. β, γ phases of Ag-Zn and β, γ phases of Cu-Sn were formed similarly. Activation energies of these phases were obtained from calculated diffusion coefficient. Activation energies were respectively 43 kcal/mol (β phase of Ni-Sn), 41 kcal/mol (β phase of Cu-Zn), 19 kcal/mol (γ phase of Cu-Zn).
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