THERMAL WAVE IMAGING AND ULTRASONIC CHARACTERIZATION OF DEFECTS IN PLASMA SPRAYED COATINGS

Disbonds at coating/substrate interface could cause premature failure of component. Current quality control test practices use empirical destructive mechanical methods that do not provide direct correlation between test results and coating performance. Non-destructive evaluation (NDE) techniques used for bulk materials are not readily adaptable for evaluation and characterization of coatings. Here use of thermal wave imaging and ultrasonic immersion C scans to characterize artificial disbonds in plasma sprayed coatings on steel substrates is reported. Work demonstrates capability in characterizing total disbonds and presence of 'kissing bonds' (where interface surfaces appear to have good bond). Effects of ultrasonic frequency on C scan images were also studied. Critical evaluation of both thermal wave imaging and ultrasonic techniques is presented along with relative advantages and disadvantages.