Method for measuring adherence of a coating on a substrate
AssigneeSnecma Moteurs
InventorsJean-Yves Francois Roger Chatellier, Daniel Sebastien Ramahefasolo
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Abstract
Ultrasound echoes (L5, L8, etc.) through the substrate (2) of a test piece (1) are collected and their amplitudes are measured, their decay being a function of the bond of a coating (2) deposited on the opposite face of the substrate (2); preliminary tests on calibration test pieces give a correlation function so that it is no longer necessary to carry out expensive and uncertain mechanical tests on the test pieces (1).
Claims4
1- Process for measuring the bond of a coating (3) on a substrate (2), characterized in that it consists of sending ultrasounds into the substrate and to the coating (3), picking up a series of echoes resulting from ultrasound reflections on faces of the substrate with an interface between the substrate and the coating, evaluating an echo attenuation coefficient (x) determining a decay in the amplitude of echoes as a function of the number of echo reflections, and deducing the said bond of a correlation function estimated in advance using calibration test pieces, between attenuation coefficients and values of the bond of the coatings determined by performing mechanical tests on calibration test pieces.
2- Process for measuring the bond of a coating on a substrate according to claim 1, characterized in that the correlation function is obtained by manufacturing several batches of calibration test pieces, the test pieces in each batch being identical, by tearing the coatings off the substrates by tension (15) while measuring the tear off resistance for each calibration test piece, and using the best tear off resistance in each of the batches as the resistance to tear off in the correlation function (σ).
3- Process for measuring the bond of a coating on a substrate according to either of claims 1 and 2, characterized in that the attenuation coefficient is a coefficient of an exponential function (A) that multiplies a distance through which ultrasounds have passed in the test piece (1).
4- Process for measuring the bond of a coating on a substrate according to any one of claims 1 to 3, characterized in that a single sensor (6) emits and receives ultrasounds perpendicular to the coating and to the substrate, and in that the coating (3) is on one face of the test piece (1) remote from the sensor.