The reactive air brazing (RAB) is a relative new brazing process, which enables to join ceramics and steel without the need of an oxygen-free atmosphere. Thus the brazing does not have to be carried out in a vacuum furnace. Due to this fact, the joining process can be realized by simple and fast heating sources such as induction coils, laser- or light-beams. One challenge of this method is to ensure, that the quality of the joints is sufficient enough to fulfil the needs of the later application. The fundamental challenge for brazing ceramics on steel is the large difference in the coefficient of thermal expansion of the ceramic, the filler metal and the steel. When cooling from the brazing temperature, this mismatch can induce high internal stresses that can cause cracks in the brittle ceramic, especially at high cooling rates. Therefore, an online monitoring during the development of RAB as well as for the later series production is of significant importance. Such a monitoring system is able to observe the processes of heating, holding and cooling during the brazing. One possible non-destructive testing method is the acoustic emission analysis which can basically detect cracks in the whole component during brazing in real time. In the presented study, the authors have integrated an acoustic emission analysis system into a RAB process. First results of the new system will be presented for the monitoring of the brazing process with respect to the melting and solidification of the solder. Another focus is the detection of cracks that may arise during the cooling phase. Finally, a review of the acoustic emission method with regard to a practical process monitoring is done.
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