Characterisation of a Plasma Beam Source During Duplex Treatment of High Speed Steel for Depositing DLC Coatings

M. Fenker , M. Balzer, N. Bermayer, Forschungsinstitut Edelmetalle & Metallchemie, Germany,

M. Rinke, M. Stüber, S. Ulrich, J. Ye, Forschungszentrum Karlsruhe GmbH, Germany

The 36th International Conference on Metallurgical Coatings and Thin Films, San Diego, California, 27. April – 1. Mai 2009

Vortrag, Carbon and Nitride Materials: Synthesis-Structure-Property Relationships, Diamond and Diamond-Like Carbon Materials, 27.04.2009

Plasma characterisation methods have been utilised to study a duplex process, consisting of plasma nitriding of high speed steel (HSS) and subsequently depositing a DLC (a-C:H) coating. Both treatments are performed by using a plasma beam source. For the plasma nitriding a gas mixture of N2/H2 was used. The nitriding duration was varied and the substrate temperatures ranged from 400 to 500 oC. The subsequent DLC deposition was performed at 100 oC with acetylene as precursor gas. The formation of a white layer could be avoided by suitable adjustment of the process parameters, resulting in well-adherent DLC coatings for nitriding depths ≥ 20 μm. Plasma characterisation methods – like optical emission spectroscopy, mass spectroscopy, Langmuir probe, electrical double probe, retarding field analyser and Faraday cup measurements – have been conducted to understand the influence of the plasma parameters on the nitriding behaviour and t he DLC film growth. The hardness of the a-C:H coatings was in the range of 1200 – 3000 HV, decreasing with increasing acetylene flow due to a decrease of the kinetic energy of the CxHy molecules impinging on the growing film surface. Raman spectroscopy showed a shifted G-peak at 1530 cm -1 and a shifted D-peak. The friction coefficients in dry pin-on-disk tests with an Al2O3 counterpart and a load of 10 N were in the range of 0.05 and 0.10. In conclusion, it could be shown that the duplex treatment with a plasma beam source has been optimised by correlating the plasma parameters with the properties of the coated parts.