Nondestructive testing of open microscopic cracks in plasma-sprayed-coatings using ultrasound excited vibrothermography

While other nondestructive testing methods hardly reveal microscopic open cracks, vibrothermography stimulated by ultrasound 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 thermal and spatial resolution infrared cameras are usually used. The aim of this work is to investigate the ability of the vibrothermography stimulated by ultrasound to detect such cracks and measure the gap between adjacent cracks. To do so, we investigated tungsten carbide coatings where cracks were artificially generated using a controlled bending test. Several samples were investigated during this study but only typical results from one sample are presented and discussed.