It is possible to diamond coat all metals in Groups IV to VI of the periodic system with melting temperatures > 700 °C (except Technetium) via microwave plasma CVD and hot-filament CVD. Stable carbide formers such as Titanium or Tungsten are easily coatable with diamond. Metals like Iron, Nickel and Cobalt with metastable carbides lead to graphite segregations and therefore the diamond layers do not adhere properly. CVD diamond grows well on precious metals (Gold, Silver, Copper), but due to the missing carbides no chemical bonding is possible. After 15 years of intense research and development of special high temperature CVD intermediate layers, it is now possible to produce strong adhering diamond coating on steel and Cobalt-Tungsten-Carbides.
CVD diamond on steel
Different steels can be CVD-diamond-coated via high temperature chrome-carbide diffusion interlayers or CVD titanium-boron-nitrides. An adjusted diamond coating temperature and heat treatment is necessary to maintain the functionality (strength) of the diamond coated steel components. The research focus lies on the expansion of the spectrum of diamond coatable steels, the optimisation of necessary steel strength and strongly adherent diamond layers with a thickness higher than 10 µm. An important application of diamond coated steel is the processing of aluminium, since aluminium does not react with the diamond surface at temperatures higher than 500 °C.
Examples:
CVD diamond on hard metals
Adherent CVD Diamond layers on hard metals are possible with titanium-boron-nitride intermediate layers. The diamond layer thickness can be higher than 100 µm. The removal of the cobalt binding phase via etching is no longer necessary, which improves the mechanical strength in the intermediate zone.
Examples:
CVD diamond on ceramics
In 1995, we started research and development of CVD diamond coatings on silicon carbide ball bearings and piston rings. In 2002 the know-how gained in Bavarian research projects was successfully transferred into industrial applications by the start-up of DiaCCon (Fürth, Germany).
Titanium- and Tantalum-based CVD coatings
Since Iron and Cobalt catalyse graphite formation during the CVD diamond deposition, high temperature intermediate layers are developed, which inhibit graphite forming on steel or hard metal surfaces. A special surface microstructure of the intermediate layer alloys a good mechanical adhesion with the subsequently growing diamond layer. In the temperature range from 500 °C to 1100 °C, CVD deposition of metallic Titanium or Tantalum layers and their carbides, nitrides or borides are possible.
Coating examples: