Influence of different interlayers and bias voltage on the properties of a-C:H and a-C:H:Me coatings prepared by reactive d.c. magnetron sputtering

Amorphous carbon (a-C:H and a-C:H:Me) films respond very sensitively to local overloads. For example, during forming tool operation, hard abrasive particles and locally high stresses on the coating surface can cause crack initiation and early coating failure. Compared to the high hardness, wear resistance and excellent friction properties, in many cases, the adhesion of a-C:H films is relatively insufficient. Furthermore, the adhesion can be clearly influenced by the substrate geometry, e.g. at sharp edges or slim substrates. Adhesion and overload resistance of a-C:H and a-C:H:Me, prepared by reactive d.c. magnetron sputtering, can be influenced in a wide range by different interlayer systems. In this study, metallic interlayers were combined with metal nitride and metal carbide interlayers. Soft metallic interlayers can reduce internal stress, prevent local overload and they can also affect the growth of the following layers. Ductile metallic nitride interlayers, especially CrN, have a supporting function, they stop crack propagation and improve the adhesion of a-C:H coatings supplementary. Additional metal–carbon gradient layers act as a mediator between the different growth structures of the interlayer system and the a-C:H top layer. Especially the influence of chromium and tungsten containing layers on the adhesion of a-C:H top layers has been investigated. Additionally, the influence of the bias voltage on the coating properties will be discussed. Two well-adapted multi-coating systems, successfully tested for highly loaded tools and components, will be presented.