Journal of the Korean Society for Nondestructive Testing (비파괴검사학회지)

The Korean Society for Nondestructive Testing (한국비파괴검사학회)
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Evaluation of the Thermal Degradation in Co-based Superalloy using High frequency Transducer of Scanning Acoustic Microscope

초음파현미경의 고주파 초음파 탐촉자를 이용한 코발트기 초내열합금강의 열화평가

  • 박익근 (서울산업대학교 NDE 연구센터) ;
  • 조동수 (서울산업대학교 NDE 연구센터) ;
  • 김용권 (서울산업대학교 에너지 환경전문대학원) ;
  • 임재생 (대한검사기술㈜) ;
  • 김정석 (고려대학교 공학기술연구소)
  • Published : 2004.10.30
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Abstract

The feasibility of Y(z) curve method of scanning acoustic microscope using high frequency transducer was experimentally studied for assessment of the thermal degradation in Co-based superalloy. Thermal degradation was performed to simulate the microstructural changes in Co-based superalloy arising from long term exposure at high temperature. Longitudinal wave velocity measured by pulse echo method using 10MHz transducer and leaky surface acoustic wave (LSAW) velocity measured by V(z) curve method using 200MHE transducer were measured to investigate the effect on thermal degradation. Ultrasonic velocity decreased as the aging time increased in both ultrasonic waves. Moreover, the low frequency longitudinal wave velocity decreased a little. Otherwise, the high frequency LSAW velocity drastically decreased up to a maximum of 4.7% at the aging time of 4,000hours. A good correlation was found between LSAW and Vickers hardness. Consequently, V(z) curve method of SAM using high frequency transducer could be a potential tool for assessing thermal degradation.

V(z)곡선법을 이용한 코발트기 초내열합금강의 열화도 평가 유용성 유무를 고주파 초음파 탐촉자를 이용하여 실험적으로 검증하였다. 코발트기 초내열 합금이 고온에서 장시간 노출되었을 때 일어나는 미세조직의 변화를 모사하기 위해서 인공열화를 실시하였다. 여로하에 미치는 초음파 음속의 영향을 고찰하고자 10 MHz를 이용하여 펄스-에코법으로 종파의 음속을 측정하고 200 MHz를 사용하여 V(z)곡선법으로 누설탄성표면파의 음속을 측정하였다. 두 초음파의 음속은 열화시간에 따라서 감소하였다 더욱이, 저주파수 종파의 음속변화는 거의 없었지만, 고주파수 누설탄성표면파의 음속변화는 열화시간에 따라서 최대 4.7%의 변화를 나타내었다. 열화에 따른 경도의 변화와 누설탄성표면파의 음속 변화는 양호한 상관관계를 나타내었다. 따라서 열화도 평가에 고주파 탐촉자를 이용한 초음파 현미경의 V(z)곡선법이 유용함을 알 수 있었다.

Keywords

References

  1. T. Kobayashi, J. Kushibiki and Chubachi, 'Improvement of measurement accuracy of line-focus-beam acoustic microscope system,' IEEE Ultrasonics Symposium, pp. 739-742, (1992)
  2. H. Kanai, N. Chubachi and T. Sannomiya,'Microdefocusing Method for Measuring Acoustic Properties Using Acoustic Microscope,' IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Vol. 39, No.5, pp. 643-652, (1992) https://doi.org/10.1109/58.156183
  3. P. A. Reinholdtsen and B. T. Khuri-Yakub, 'Image Processing for a Scanning Acoustic Microscope That Measures Amplitude and Phase)' IEEE transactions on ultrasonics, ferroelectrics and frequency control, Vol. 38, No.2, pp. 141-147, (1991) https://doi.org/10.1109/58.68471
  4. M. Duquennoy, M. Ourak, W. J. Xu, B. Nongaillard and M. Ouaftouh, 'Observation of V(z) curves with multiple echoes,' NDT & E International, Vol. 28, No.3, pp. 147-153, (1995) https://doi.org/10.1016/0963-8695(95)00006-J
  5. D. Coutsouradis, A. Davin and M. Lamberigts, 'Cobalt-based Superalloys for Applications in Gas Turbines)' Mat. Sci. and Eng., Vol. 88, pp. 11-19, (1987)
  6. W. H. Jiang, H. R. Guan and Z. Q. Hu, 'Effects of heat treatment on microstructures and mechanical properties of a directionally solidified cobalt-base superalloy,' Mat. Sci. and Eng., Vol. 271, pp. 101-108, (1999)
  7. G. Johnson and R. Truell, 'Numerical computation of Elastic Scattering Cross Sections)' J. Appl. Phys., Vol. 36, pp. 34663475, (1965)
  8. R. H. Latiff and N. F. Fiore, 'Ultrasonic attenuation in spherodized steel,' J. Appl. Phys., Vol. 45, pp. 5182-5186, (1974) https://doi.org/10.1063/1.1663213
  9. F. Bergner, B. Kohler and K. Popp, 'The Role of Microstruture in the Propagation of Ultrasound in Bainitic Low-Alloy Steels)' Int. J. Pres. Ves. & Piping, Vol. 55, pp. 251-260, (1993)
  10. F. Fouquet, P. Merle and M. Kohen, 'Comments on An investigation of the precipitation-hardening process in aluminum alloy 2219 by means of sound wave velocity and ultrasonic attenuation)' Mat. Sci. Eng., Vol. 57, pp. 261-262, (1983)
  11. A. Kumar, B. K. Choudhary, T. jayakumar, K. B. S. Rao and B. Raj, 'Characterization of long term aging behavior of 9Cr-1Mo ferritic steel using ultrasonic velocity', Mat. Sci. Tech., Vol. 19, pp. 637-641, (2003)