Non-destructive thickness determination of metallic coatings using ultrasonic Leaky Rayleigh waves
This paper presents a non-destructive method based on the measurement of ultrasonic Leaky Rayleigh waves characteristics (velocity and attenuation) for the thickness measurement of vacuum plasma sprayed (VPS) NiCoCrAlY coatings deposited on AISI316L and Ni-based substrates which are used to protect gas turbine blades against high temperature corrosion and erosion phenomena. The ultrasonic technique used is based on the measurement of an acoustic signature (the so-called v(z)-curve) of the coated specimen. Two highly-damped flat transducers (one working as a transmitter, the other as a receiver) are translated along a z-axis, perpendicular to the sample surface. The sample is immersed in water. For each height z of the transducer, the received signal is digitised and Fourier transformed. Thus, for each frequency, complex v(z)-curves are obtained. By choosing the dimensions of the beam appropriately, the height z and the frequency, the variations of the amplitude and of the phase allow the measurement of the thickness. The method was applied to different substrates coated by a NiCoCrAlY layer with the thickness ranging from 60 to 330 micron. The ultrasonic layer thickness was then successfully correlated to the one optically measured on cross-section micrographs.
Bibliographic Reference: Paper presented: 7th International Symposium on Non-destructive Characterisation of Materials, Prague (CS), June 19-23, 1995
Availability: Available from (1) as Paper EN 38985 ORA
Record Number: 199510718 / Last updated on: 1995-07-07
Original language: en
Available languages: en