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Carbon based coating systems for forming tools

: Weber, M.; Bewilogua, K.; Bialuch, I.; Keunecke, M.; Thomsen, H.; Wittorf, R.

Society of Vacuum Coaters -SVC-, Albuquerque/NM:
Society of Vacuum Coaters. 49th Annual Technical Conference 2006. Proceedings : April 22 - 27, 2006, Washington, D.C. USA
Albuquerque: SVC, 2006
Society of Vacuum Coaters (Annual Technical Conference) <49, 2006, Washington/DC>
Conference Paper
Fraunhofer IST ()

Since many years titanium based hard coatings have been routinely applied for forming tools to increase their lifetime drastically. The rising use of stainless steel, aluminum and magnesium causes new requirements for coatings e.g. on pressing tools because the potential of conventional hard coatings to reduce cold welding is limited in these cases. At the Same time there is a cleas demand to reduce or eliminate the use of lubricants and separation agents.
Amorphous carbon (a-C:H and a-C:H:Me) films have a high potential to fulfill these requirements. Nevertheless, compased to the high hardness, wear resistance and excellent friction properties, in many cases the life time of a-C:H films is relatively insufficient. 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.
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 inter-layer systems. Especially ductile metallic nitride inter-layers, like CrN, have a supporting function and they stop crack propagation. Additional metal-carbon gradient layers can improve the adhesion of a-C:H coatings supplementary. Two well adapted multi-coating systems, successfully tested for aluminum and magnesium forming, will be presented. The homogeneity of the coatings depending on the geometry of the substrates and their mounting positions relative to the targets will be discussed.