TITLE

An experimental study of microstructure-induced ultrasonic signal fluctuations in jet-engine titanium alloys

AUTHOR(S)
Margetan, Frank J.; Wasan, Harpreet; Thompson, R. Bruce
PUB. DATE
May 2000
SOURCE
AIP Conference Proceedings;2000, Vol. 509 Issue 1, p1433
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Ultrasonic echoes from identical defects in a metal component will vary due to the influence of the local microstructure in which each defect is embedded. Two effects are responsible: (1) the scattering of sound at nearby crystallite boundaries results in “grain noise” which is superimposed on the defect echo; and (2) the intervening microstructure modulates or distorts the sonic field that is incident on the defect, thus modifying its echo. Both effects can be significant in engine titanium alloys, and both influence inspection reliability. In this work, a series of experiments is performed to investigate signal fluctuations primarily arising from the second effect. Arrays of nominally identical #1 flat-bottomed holes (FBHs) in Ti-17 and Ti 6-4 specimens are scanned using a 10-MHz, broadband, focused transducer. The peak echo amplitude of each FBH in the array is measured, and the ratio of the standard deviation of the peak amplitudes to their mean serves as a dimensionless measure of the fluctuation level. Similar measurements are performed on a fine-grained nickel specimen that serves as a reference. The fluctuation level and the apparent average ultrasonic attenuation are measured as functions of alloy, propagation direction, frequency, and inspection water path (i.e., degree of beam focusing). In addition, beam distortions are studied by analyzing the sizes and shapes of the C-scan images of the FBHs.—Specimens used in this work were supplied by the Engine Titanium Consortium under the Federal Aviation Administration Grant No. 94-G-048. © 2000 American Institute of Physics.
ACCESSION #
6029238

 

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