Combination of scratch-test and acoustic microscopy imaging for the study of coating adhesion

The scratch-test is particularly well suited for the characterization of the adhesion of thin films and acoustic microscopy imaging for the in-depth observation of defects through opaque materials. This work proposes an original combination of these two different techniques for the study of adhesion of thick ductile coatings electrodeposited on a relatively rough substrate, as a function of surface preparation. On the tangential force curve, two distinct transitions have been recorded as a function of displacement along the scratch and correlated with substrate preparation. Interface acoustic images of scratches show pronounced acoustic contrast due to the propagation of delamination around the scratch. This is the only technique capable of imaging such interface defects which are due to the stress induced by the scratch experiment. The delaminated area was measured in these images and could be correlated with coating adhesion. The complementarity of the two methods used is emphasized. The combined approach described in this paper should be useful for the characterization of many other film-substrate systems.