Chemical vapour deposition of polycrystalline diamond films on steel substrates

Direct coating of polycrystalline diamond films on steel substrates by conventional activated chemical vapour deposition methods is not possible. Minimum substrate temperatures around 700 deg C used for diamond deposition cause a decrease in Rockwell and Vickers hardness of more than 35 per cent of the original HRC and HV10 values, respectively. Additionally at temperatures below 500 deg C, the interaction between the activated hydrogen gas phase and the steel surface leeds to embrittlement, which becomes noticeable by cracks after indentation. Under diamond deposition conditions the interdiffusion between substrate and deposited carbon material also changes the mechanical properties of the substrate and hinders the formation of diamond. To apply highly wear resistant polycrystalline diamond coatings on high speed steel tools we investigated the use of silicon carbide interlayers as well as nitriding pretreatment of the substrate.