Christian Stein, Markus Höfer, Sarah Baron, Markus Armgardt, Daniel Schulze, Tino Harig, Volker Sittinger, Fraunhofer Institute for Surface Engineering and Thin Films IST, Braunschweig, Germany
Diamond has fascinated mankind for centuries due to its unique appearance and outstanding mechanical, electrical, thermal and chemical properties. For heavy-duty components and high-performance cutting and forming tools, the enormous hardness of up to 10,000 HV, the corresponding high wear resistance and the chemical inertness in contact with many workpiece materials offer desirable advantages for innovative products with a long service life. However, making diamond materials technically feasible for industrial applications at acceptable production costs is a major challenge. A very material- and cost-efficient option is the deposition of comparatively thin diamond coatings with typical thicknesses ranging from a few microns to a few tens of microns by CVD technologies. Hot-filament CVD (HFCVD) is commonly used to economically coat complex tools and large machine components. Fully automated HFCVD systems can coat areas up to 1000 x 500 mm^². Possible base materials include cemented carbides, ceramics (especially SiC, Si₃N₄, AlN), refractory metals, silicon, quartz and sapphire. For the successful application of diamond coatings, the entire process chain must be considered, starting with component/tool design and material selection, through cleaning, pre-treatment and seeding, to coating design and deposition process. This presentation will give an overview of different types of diamond coatings, such as micro- and nanocrystalline diamond, the associated HFCVD production technology, possible options and given limitations. Particularly for tools, a key aspect is to achieve good diamond quality and adhesion on cemented carbide, which is currently the most commonly used base material. The conventional treatment sequence for the coating of cemented carbide involves the reduction of the binder in the near-surface region by chemical etching, since elements such as Co, Ni and Fe are detrimental to the nucleation and growth of diamond. As an alternative to etching treatments, interlayer systems that act as a barrier to the diffusion of binder elements are discussed. Finally, various industrial applications of diamond coatings for tools in cutting and forming operations as well as for high-end mechanical face seals will be shown and present and future research topics will be presented.