Grain boundary penetration behavior analysis of OFC brazed with AgCu28 brazing filler

Repeated use of eutectic AgCu28 solder can cause performance degradation in the base material due to grain boundary penetration. To gain further understanding of this phenomenon, thus providing comprehensive data and technical guidance for greater reliability during production of vacuum devices, the microstructure and composition of oxygen-free copper (OFC)-Nickel-plated steel, OFC-Monel, and OFC-OFC brazed joints using AgCu28 brazing filler was observed through SEM and optical microscopy. Results show that the brazing filler in the OFC-OFC brazed joints is securely soldered to the joints' microstructure, and the microstructure is very condensed. However, the filler in the brazed joints of OFC-Nickel-plated steel and OFC-Monel diffuses along the OFC boundary, showing very apparent grain boundary penetration in the brazed joints. Ingredient analysis show that during soldering, the Ni element in Ni-containing base metal dissolves into the brazing filler rapidly. It is surmised that the dissolving of Ni element in the brazing filler is the main reason leading to grain boundary penetration.