Quality Control of Hard Coatings

by Scratch Testing


Ceramic coatings deposited by PVD (Physical Vapour Deposition) or CVD (Chemical Vapour Deposition) techniques, designated here as “hard coatings”, are used in general for their wear and corrosion resistant properties and/or low friction properties. Different parameters (composition, microstructure, thickness, internal stresses, adhesion strength, hardness, ductility, toughness, thermal stability) would influence their wear and friction properties as well as their chemical resistances.

Figure 1: Typical applications of PVD coatings: cutting tools and inserts

Different methods of testing have been used for the characterization of the mechanical properties of hard coatings. Tribological measurements provide useful information on the essential properties related to their final use in real applications, i.e. coefficient of friction and wear. Instrumented indentation testing provides information on hardness and elastic modulus of the coatings. But none of these methods would give meaningful information on the control quality of the deposition process. Scratch testing is measuring the adhesion and scratch resistance of coatings and providing unmatched information on the mechanical integrity of the coating-substrate system. Different aspects for the scratch test method for quality-control are detailed in this Application Note.

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