Failure mode analysis in the scratch test of hard PVD coatings. Part 2: experimental and influence of substrate roughness

The scratch test has been used for many years to provide a measure of coating/substrate adhesion. In the conventional configuration of the test, a diamond stylus (usually Rockwell C) is drawn across the coated surface under an increasing load until some well-defined failure occurs at what is often referred to as the critical loads, Lc1, Lc2, Lc3. Many different failure modes are observed which include coating detachment, through-thickness cracking and plastic deformation or cracking in the coating or substrate. Even though the failure modes observed during scratch test depend on many factors, the main parameters that influence the failure modes are the substrate hardness and the coating hardness. With respect to such parameters, a model was developed to determine failure modes maps [1, 2] providing information on which of the different failure mode will occur for determined values of substrate and coating hardness. However little experimental work has been made in order to give experimental proof of the model prediction, as well as to include other parameters in the failure mode prediction.