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

• Published in: Advanced engineering materials 2021-02, Vol.23 (2), p.n/a
• Main Authors: Waetzig, Katja, Schilm, Jochen, Mosch, Sindy, Tillmann, Wolfgang, Eilers, Arne, Wojarski, Lukas
• Format: Article
• Language: English
• Subjects: ceramic–metal joints; reactive air brazing; silver-copper oxide metal fillers
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.202000711

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. Reactive air brazing (RAB) is a cost‐effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air without protective gas atmosphere or a vacuum. Pore‐free brazing seams between filler metal and steel of metal–ceramic joint are achieved by selected steel and filler composition by induction heating in a conventional muffle furnace under air.