Ultrasonic assessment of coatings dispersion curves by microdefocusing

LAIN, University Montpellier 2, Place Eugène Bataillon, CC082, 34095 Montpellier Cedex 05, France

Corresponding author: laux@lain.univ-montp2.fr

Received: 21 September 2004
Revised: 9 May 2005
Accepted: 24 June 2005
Published online: 15 September 2005

Abstract

In 2001 we have published a paper [1] in which an ultrasonic method using a large bandwidth transducer with a spherical lens and based on acoustic waves separation near the focal region was presented. We have shown that compared to traditional acoustic microscopy (acoustic signature) the size of the zone analysed on bulk samples was highly reduced. This method is now extended to thin films on bulk substrates. Experimental dispersion curves for thin DLC (Diamond Like Carbon) films on steel are presented. The ultrasonic velocity of leaky Sezawa mode is assessed on a large bandwidth even in zones where the transducer is not very efficient. We show that the signal processing used enlarges the frequency domain explored. Such an element is essential for inverse problem treatment and coating elastic modulus calculation. Once again we show that the length of defocusing can by highly reduced. Hence, the zone analysed on the sample is smaller.