Schematic Diagram of the Sample (Top) and the photographs of the sample (Bottom)

Amplitude thermal image: The surface and emissivity variations clearly manifest on the surface

Phase thermal image: Apart from the notch, the debonded region indicated by the ellipse can be clearly seen.
The thermal imaging system model Silver- 420 of M/s CEDIP (now FLIR Systems), France with pulsed and lockin thermography facility was used for the study. It was carried out at Indira Gandhi Centre for Atomic Reasearch, Kalpakkam, India.

To confirm the observations of lock in, high sensitivity radiography and ultrasonic examination of the specimen surface was also carried out.

Digitised Radiographic Image of Colmonoy Sample: Radiography could reveal the flat bottom hole and notch but not the debonded region.

Ultrasonic Examination: Multiple back wall reflections from a good region (left) and Indication of debonding when the probe is placed at the coating. Compared to ultrasonics, the main advantage of lock in thermal imaging is that it is a whole field technique and an entire area can be covered in a single step. The examination time is also quite small. No surface preparation or cleaning is required.