Characterisation of Colmonoy Coatings using Lock-In Thermography
Hard facing alloys like Colmonoy are overlaid on nuclear components to provide corrosion,wear and galling resistance under high temperature service conditions. Typical reactor components on which overlays are provided include grid plate, diverse safety rod drive mechanism etc. The thickness of the overlay ranges from 0.5-3 mm. Typical defects likely during deposition include lack of bonding between substrate and overlay, cracks and porosities. Conventionally ultrasonic, LPT and radiography has been used for the process qualification and on the actual components. It is well established that thermal imaging can be used for detection of detects especially lack of bonding and materials characterization. Conventionally active techniques such as pulsed thermal imaging have been employed. This paper highlights the successful application of lock-in thermography for characterization of colmonoy coatings. The main advantage of lock in technique is that it is unaffected by emissivity variations and also defect depth can be estimated. A Silver-420 system with pulsed and lock in thermography was used for the study. A sinusoidal signal was used and the frequency of modulation varied from 0.05 Hz -0.5 Hz. The images were acquired at a frame rate of 50 Hz and the integration time was 1600μs. The sample consisted of Colmonoy coating (2-3mm) on a 316 LN substrate. 5% notch and 2??flat bottom holes were introduced on the Colmonoy coated side for calibration. The phase and the amplitude images were analysed. It was observed that the average phase angle could be clearly used for detecting thickness variations and presence of debonds in the specimen. The results were correlated using ultrasonic techniques. Results clearly indicate the superior defect detectability and quantization by lock in method especially for coatings. This paper presents in detail the experimental methodologies, challenges and also the results of the investigation.
Colmonoy coating lock-in thermography ultrasonics
B.Venkatraman M.Menaka R.Subbaratnam Baldev Raj
Indira Gandhi Centre for Atomic Research Kalpakkam - 603 102, India
国际会议
第十七届世界无损检测会议(17th World Conference on Nondestructive Testing)
上海
英文
1809-1814
2008-10-25（万方平台首次上网日期，不代表论文的发表时间）