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6000 |
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Wednesday, May 22, 2019, Saal Brüssel 4:00 PM Brazing of ceramic and glass |
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Reactive air brazing of ceramic-steel composites with novel composition of brazing pastes |
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Katja Waetzig* / Fraunhofer IKTS, Germany Jochen Schilm / Fraunhofer IKTS, Germany Matthias Manka/ TU Dortmund University, Germany Wolfgang Tillmann/ TU Dortmund University, Germany Arne Eilers/ TU Dortmund University, Germany Norman Sievers/ TU Dortmund University, Germany |
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Reactive air brazing of ceramics based on Ag-CuO type filler metals is a cost-effective way to produce ceramic-ceramic or ceramic-metal composites at air, without applying a protective gas atmosphere or a vacuum. In addition to furnace technology, brazing by means of induction heating can also be used effectively. A considerable disadvantage of reactive air brazing is still the formation of pores or cavities in the brazing seams, the reasons for their emergence only partially being clarified. Besides an incomplete debinding of the brazing pastes, an insufficient wetting of the pastes as well as intrinsic side reactions of filler metals are discussed as possible origins of the defects. Sintering investigations on different silver powder qualities revealed significant reboil effects at high temperatures, leading to an expansion of densified powder compacts, caused by evolving gases. Against this background, systematic variations of the brazing pastes concerning the copper type and content, the type of silver powder, and binder components have been formulated within this study. The sintering and wetting behavior of these reactive air brazing pastes were investigated by means of hot stage microscopy on various ceramic materials such as different grades of Al2O3, ZTA and ZrO2. Joining tests were conducted on ceramic-ceramic and ceramic-steel composites by using muffle furnaces and an induction heated sample holder for short brazing cycles. The joint composites were investigated using non-destructive ultrasonic microscopy as well as scanning electron microscopy to investigate the microstructures in the brazing zones and interfaces. As a result, correlations between the filler metal composition, type of ceramic material, and brazing conditions were obtained. |