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Proceedings Paper

Nondestructive inspection of open micro-cracks in thermally sprayed coatings using ultrasound excited vibrothermography
Author(s): Jean-Marc Piau; Abdelhakim Bendada; Xavier Maldague; Jean-Gabriel Legoux
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Paper Abstract

While other non-destructive testing methods hardly reveal microscopic open cracks, ultrasound excited vibrothermography provides very promising results by converting mechanical waves into local heat by friction. This phenomenon enhances thermal gradients in temperature maps as compared to conventional techniques. To detect temperature gradients caused by hidden cracks, high temperature and spatial resolution infrared cameras are usually used. Recently, it has been shown that the HVOF (High Velocity Oxy Fuel)-spraying of tungsten carbide or cobalt coatings onto steel substrates, seems to be a suitable alternative to the non-environmentally friendly chromium coating material. However one major issue with these thermal-sprayed coatings is the possibility of the appearance of microscopic cracks when they are submitted to excessive bending loads. If the open cracks spread through the whole coating thickness (typically 100 to 200 ?m), they might also propagate at the coating-substrate interface causing the coating to delaminate in between adjacent open cracks. The latter disbonding phenomenon is therefore strongly dependent on the distance between adjacent open cracks. Therefore, a non destructive technique enabling the detection of cracks and the evolution of their density is critical to preserve the components integrity. The aim of this work is to investigate the ability of ultrasound excited vibrothermography to detect such cracks. To do so, we investigated tungsten carbide coatings where cracks were artificially generated using a controlled bending test. Results on different samples are presented and discussed.

Paper Details

Date Published: 9 April 2007
PDF: 9 pages
Proc. SPIE 6541, Thermosense XXIX, 654112 (9 April 2007);
Show Author Affiliations
Jean-Marc Piau, Laval Univ. (Canada)
Abdelhakim Bendada, Laval Univ. (Canada)
Xavier Maldague, Laval Univ. (Canada)
Jean-Gabriel Legoux, Conseil national de recherches (Canada)

Published in SPIE Proceedings Vol. 6541:
Thermosense XXIX
Kathryn M. Knettel; Vladimir P. Vavilov; Jonathan J. Miles, Editor(s)

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