4 Real Time NDE of Cold Spray Processing Using Acoustic Emission 35 Fig. 4.7 AE for 90Ta-10W containing large agglomerates sprayed on aluminum, where a delamination occurred. Top plot is the WD sensor, bottomis the 30 sensor. Periods correspond to following: (A) nitrogen purge, (B) helium purge, (C) powder deposition with fairly high amplitude AE, (D) a second period of powder deposition leading up to delamination as shown by the arrow, and (E) a period of poor coating (there were small fragments spalling from the deposit) leading up to the powder running out, (F) a period when the nozzle was still making passes on the substrate with no powder in the hopper, and (G) movement of the nozzle away from the surface and conclusion of the test 4.5 Conclusion This work has shown that AE is a promising technology to monitor the cold spray process in real time. Specifically, AE was used to detect changes to the gas flow, impacts from large particles which could be present in feedstock, delamination of coating, and also to determine when powder is exhausted. Hence, the use of real time AE diagnostics would also be beneficial for other types of additive manufacturing processes (i.e. high velocity oxy fuel, plasma spray deposition, laser sintering). However, much work remains to be done in the area, which will need to focus upon optimizing the system parameters and instrumentation, tailoring the signal conditioning system to address the high noise, performing source location analysis to assist in defect isolation, and working more with NOESIS to better characterize the multiple sources of AE in this challenging application of the technology. Acknowledgements The authors thank the United Technologies Research Center for support of this study and permission for publication.
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