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Non-destructive evaluation of brazed joints by means of acoustic emission

: Traxler, H.; Arnold, W.; Knabl, W.; Rödhammer, P.

Journal of Acoustic Emission 20 (2002), S.257-264
ISSN: 0730-0050
European Conference on Acoustic Emission Testing (EWGAE) <25, 2002, Prag>
Konferenzbeitrag, Zeitschriftenaufsatz
Fraunhofer IZFP ()
acoustic emission; nondestructive testing; brazing; x-ray target

Brazing is a key technology in the production of components made of high performance ma- terials. Due to the extreme operating conditions and stringent safety requirements, there is a strong demand for quality assurance by non-destructive evaluation of brazed components such as composite X-ray targets. An established method for non-destructive testing is ultrasonic C-scanning in the pulse-echo mode. This method allows one to detect voids in the brazing interface such as voids, which are caused by inhomogeneous wetting by the filler metal of the parts to be brazed. Additionally there is an interest for the microstructure of the braze alloy and for testing its loading capacity. To get information on these properties at present metallography or loading tests up to destructive load levels are required. The results presented here show that acoustic emission (AE) during a loading test to a subcritical load level is sensitive to deviations in the process parameters causing embrittlement of the brazing alloy. The origin of the AE signals has been identified by the systematic exclusion of the various possible sources in a comparative ex- perimental study. Furthermore, a correlation between the non-destructive AE test and the destructive load test has been established. Samples, which failed prematurely in the destructive load test, showed a strongly increased signal rate and a specific type of signals in the AE test.