Verein Deutscher Ingenieure

PVD and CVD hard coatings - Quality assurance - Characteristic profiles and fields of application of hard coatings
 N VDI 3824 BLATT 1

Annotation

The coating of tools is currently the principal application of hard coatings. Also, hard coatings are increasingly applied to components and parts in the fields of general mechanical engineering, medical technology, and in the consumer-goods industry, in order to protect them from wear, to reduce friction, and for decorative purposes.

Hard coatings consist of materials the hardness of which is typically higher than that of hard metal because of the lack of a relatively soft metal matrix phase. These materials are mainly produced from the vapour phase, using nitrides, carbides, borides, and oxides of the metals Ti, Cr, W, Al, and Zr, and mixtures of these. Furthermore, hard carbon coatings have gained great importance.

For the deposition of hard coatings, PVD (physical vapour deposition) and CVD (chemical vapour deposition) processes are applied, with and without plasma enhancement. The processes are described in the guideline VDI 3198 "Coating (CVD, PVD) of cold forging tools", and, in greater detail, in the guidelines VDI 3824 Part 2 "Requirements to be met by tools and components to be coated", and Part 3 "Production processes and procedures".

The application performance of the hard-coating/substrate composite created by the coating process is a system characteristic resulting from the combination of the characteristics profiles of the coating and substrate materials. The characteristics profile of the coating is determined by the characteristics of the coating material and by the performance of the coating as part of the composite in the relevant application (e.g. in a specific tribological system consisting of body, counter body, interfacial medium, and surround medium; DIN 50 323-2). The composite created by coating allows a functional distinction between surface and volume characteristics. For this reason, the basis material and its surface condition shall be matched with the coating system carefully. For instance, the surface condition of the basis material directly influences the transition zone, and thus the adhesion between hard coating and substrate.