Abstract
Ultrasonic surface waves are suitable for the characterization of surface hardened materials. This is shown on laser hardened turbine blades. The martensitic microstructure within the surface layer of surface hardened steels has a lower surface wave propagation velocity than the annealed or normalized substrate material. Because the propagation velocity depends on the ratio of layer thickness to wavelengthd/λ, its measurement allows the determination of the hardening depth. If the surface wave frequency is high enough, the surface wave propagates mainly within the hardened layer. A correlation of the surface wave velocity to the surface hardness has been found. Because the variation of the surface velocity in hardened steels is small, a high measurement accuracy is necessary to obtain the interesting hardening parameters with sufficient certainty. Therefore, a measuring arrangement has been developed where laser pulses, guided by optical fibers to the surface hardened structure, generate simultaneously surface wave pulses at two different positions. The two ultrasonic pulses are received by a piezoelectric transducer. The surface wave velocity is obtained from the time delay between these pulses which is determined by the cross-correlation method. To evaluate simultaneously surface waves with different penetration depths from the same signal acquisition, digital filtering has been used in connection with the cross-correlation.
Similar content being viewed by others
References
B. Brenner, G. Wiedemann, B. Winderlich, S. Schädlich, A. Luft, W. Reitzenstein, W. Storch, D. Stephan, and H.-T. Reiter, inLaser Treatment of Materials, B. L. Mordike, ed. (DGM-Informationsgesellschaft Oberursel, 1992), pp. 199–204.
B. A. Auld,Acoustic Fields and Waves in Solids (Vol. II, Chap. 10) (John Wiley & Sons, New York, 1973).
G. W. Farnell and E. L. Adler, inPhysical Acoustics (Vol. IX), W. P. Mason and R. N. Thurston, eds. (Academic Press, New York, 1972).
E. P. Papadakis,Int. Met. Rev. 29:1 (1984).
B. R. Tittmann, L. A. Ahlberg, J. M. Richardson, and R. B. Thompson,IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (Vol. UFFC-34) (1987), p. 500.
J. Krautkrämer and H. Krautkrämer,Ultrasonic Testing of Material (Springer-Verlag, Berlin, 1990).
D. Schneider and B. Brenner, European Patent No. EP 0471239 A2.
J. Huang and J. D. Achenbach,J. Acoust. Soc. Am. 90:1269 (1991).
D. R. Hull, H. E. Kautz and A. Vary,Mater. Eval. 43:1455 (1985).
A. H. Quazi,IEEE Transaction on Acoustics, Speech, and Signal Processing, ASSP-29 (1981), p. 527.
J. D. Aussel and J. P. Monchalin,Ultrasonics 27:165 (1989).
C. W. Helstrom, Statistical theory of signal detection, inInternational Series of Monographs in Electronics and Instrumentations (Vol. 9) (Pergamon Press, Oxford, 1968).
D. Schneider and B. Brenner,Neue Hütte 34:374 (1989).
I. A. Victorov,Rayleigh and Lamb Waves (Plenum Press New York, 1987).
D. Schneider, H. J. Scheibe, Th. Schwarz, and P. Hess,Diamond Rel. Mater. 2:1396 (1993).
D. Schneider, Th. Schwarz, and B. Schultrich,Thin Solid Films 219:92 (1992).
D. Schneider, B. Brenner, and H. Ollendorf (to be published).
G. V. Kurdjumov,Iron Steel Inst. 195:26 (1960).
E. Schmidtmann, E. Hougardy, and H. Schenk,Arch. Eisenhüttenwes. 36:191 (1965).
D. Schneider, K. Herrmann, B. Brenner, D. Schläfer, and B. Winderlich,Cryst. Res. Technol. 21:897 (1986).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Schneider, D., Brenner, B. & Schwarz, T. Characterization of laser hardened steels by laser induced ultrasonic surface waves. J Nondestruct Eval 14, 21–29 (1995). https://doi.org/10.1007/BF00735668
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00735668