Microstructure and properties of the joints of Cu/Cu and metallized Cu / kovar brazed with a low-silver vacuum brazing filler metal

In an attempt to develop low-silver brazing filler metals used for hermetic sealing materials in the vacuum interrupter industry, the ternary Ag-50Cu-5Ga low-silver vacuum brazing filler metal was investigated. The melting temperature was measured by differential scanning calorimetry (DSC), and the brazability of Ag-50Cu-5Ga alloy on copper and metallized copper/kovar were ascertained at 850 ℃ under 1 × 10^–4 Pa in this article. The microstructures of the filler metal and the joints have been analyzed by using scanning electron microscopy (SEM), equipped with an energy dispersive spectroscopy. The results show that vacuum brazing was success to join with copper or metallized copper/kovar using Ag-50Cu-5Ga filler and reliable joints were obtained. There were Ag-rich phase, Cu-rich phase and a fine eutectic structure of Ag-based solid solution and Cu-based solid solution in the copper joints and the width of brazing seam is about 60 μm. The joints of kovar alloy to copper after surface nickel plating was composed of AgCu eutectic phase, Ag, Cu, Cu₂Ga and CuNi₂ phase. The tensile strength was 167 MPa and 150 MPa, respectively. The tensile results of joints show that the joint strengths were equivalent to the traditional brazing filler metals.