Influence of the Brazing Paste Composition on the Wetting Behavior of Reactive Air Brazed Metal–Ceramic Joints

Abstract

Reactive air brazing (RAB) is a cost-effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air, without applying a protective gas atmosphere or a vacuum. In addition to conventional furnace technology, the brazing with induction heating can also be used effectively. Within the scope of this study the shrinkage and wetting behavior of self-developed brazing pastes with different CuO contents and two qualities of silver powders with coarse and fine particle size are investigated by optical dilatometry on alumina (Al2O3, 99.7% purity). Thereby, the fine silver powder quality reveals a significant swelling effect at high temperatures, leading to an expansion of densified powder compacts caused by evolving gases. Joining tests are performed on ceramic–steel brazed joints using a muffle furnace and induction heating for short brazing cycles. The brazing seams and interfaces of the joints are investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). As a result, correlations between the brazing filler metal composition, the steel, and the brazing conditions are obtained.