Nondestructive testing of ceramic coatings on steel by photoacoustic, photothermal and high-frequency ultrasound techniques

Adhesion of tungsten carbide coatings with a thickness of about 300 fm on steel subtrates has been tested by photoacoustic microscopy at 33.8 kHz, by photothermal raiometry at 20-200 Hz and by high-frequency ultrasound measurements at 80 MHz. Delaminated regions of the coating were detected in good agreement with the photoacoustic and the ultrasound technique.