Materials Transactions Online

Materials Transactions, Vol.53 No.04 (2012) pp.671-675
© 2012 The Japan Institute of Metals

Detection of AE Events due to Cracks in TBC during Spraying Process

Kaita Ito1, Hitoshi Kuriki1, Makoto Watanabe2, Seiji Kuroda2 and Manabu Enoki1

1Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
2National Institute for Materials Science, Tsukuba 305-0047, Japan

Cracks may occur inside a top coating or at an interface between the top and bond coating of the thermal barrier coating (TBC) during atmospheric plasma spraying (APS) process. The acoustic emission (AE) method is suitable for detection of the generation and propagation of these cracks because it is an in-situ non-destructive evaluation technique. However, AE monitoring of APS process is prevented by large acoustic noise at elevated temperature on a specimen due to heating by the plasma jet. Therefore, a non-contact laser AE method with a newly developed measurement and analysis system was used for monitoring of the top coating process. Several types of noise reduction processes such as soft-thresholding were applied to continuously recorded AE waveform. Experiments were conducted with various preheating temperatures and scanning speeds of the plasma torch. AE events due to cracking were detected only during spraying, on the other hand no events were detected after spraying. The effect of preheating temperature and scanning speed of the plasma torch on the development of cracks were estimated. A correlation was observed between the density of delamination cracks and the number of AE events.

(Received 2011/11/29; Accepted 2012/01/31; Published 2012/03/25)

Keywords: atmospheric plasma spraying, laser acoustic emission method, thermal barrier coatings, signal processing

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