Ultrasonic Inspection of Ceramics Containing Small Flaws.

摘要

A 45MHz ultrasonic shear wave technique was developed and evaluated for detection of small defects,less than 100micrometers(0.004inches),in gas turbine quality ceramics. Results for the shear wave technique were compared with the results for the previously developed 45MHz longitudinal wave technique on hot pressed silicon nitride and silicon carbide from two vendors and on boron-doped sintered silicon carbide. Conventional mechanical tests were also performed to verify defect sizes and types and to correlate material strength with ultrasonic inspection results. The shear wave technique was found to have better sensitivity than the longitudinal wave technique,and specimens whose failure initiated at defects detected by the shear wave technique showed significantly lower strength than those whose cause of failure was undefined. Investigation of inspection frequencies up to 75MHz revealed the need for instrumentation and transducer performance improvements in order to achieve the potential for higher defect detection sensitivity.