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In this paper, recent results on the synthesis of diamond coatings on cemented tungsten carbide substrates (WC–Co) with photon plasmatron are presented. This new plasma-CVD method for high-rate diamond synthesis in the open-air atmosphere has been described in a previous paper [S. Metev, H. Brecht, J. Schwarz, G. Sepold, New technology for high-rate synthesis of PC-diamond coatings in air with photon plasmatron, Diamond and Rel. Materials, 11 (2002), p. 472]. In the course of the work, the influence of the outstanding plasma parameters and deposition conditions (plasma temperature 15.000–20.000 °C, high ionization degree, operating pressure ≥1 atm, deposition rates of 12 up to 60 μm/h) on the film properties have been investigated. Special emphasis has been laid out on the influence of the composition and the properties of the substrate material. The latter varied concerning the WC–Co ratio, grain size and surface roughness. The presence of the binder phase Co is a well-known handicap for the deposition of adhesive diamond coatings. Therefore, selected pretreatment methods (grinding, etching, ultrasonic baths, seeding) in combination with the specific deposition conditions have been used to optimize the film properties. Effects of the substrate pretreatment and the film properties have been characterized by analytical methods, including SEM, EDX, RAMAN, Profilometer and scratch testing.

In this treatment method laser radiation, which is guided from a co-axially expanding liquid jet-stream, locally initiates on a metal surface a thermochemical etching reaction, which leads to selective material removal. Time-resolved measurements of the electrical potential were correlated with the specific processing parameters to identify conditions for stable and enhanced chemical etching reactions. The chemical etching reaction was additionally influenced by an electrical field. Depending on its polarity a significant increase in the etch rate or improvement of the treatment quality was observed. Exemplary, the fabrication of superelastic micro-grippers prepared by cutting of temperature-sensitive shape memory alloys is shown.

In this paper the development of a new plasma-CVD method for synthesis of PC-diamond coatings in air is presented. The method does not require any vacuum or reaction chamber and is based on plasma-CVD processes taking place in a photon-initiated stationary plasma in the open-air atmosphere maintained in the electromagnetic optical field of a high-power cw-CO 2 laser radiation. To use this plasma as an activation source for the CVD process with different gas precursors, a special photon plasmatron operating in air has been designed and constructed. The high temperature in the photon-initiated plasma (15 000–20 000 K) as well as the high pressure (≥1 atm) of the precursor gases, are prerequisites for a high-rate synthesis of PC-diamond coatings. For this purpose, different gases like Ar, CO 2 , CH 4 , H 2 , N 2 and their mixtures have been used. The properties of the deposited coatings in dependence on the experimental conditions have been investigated with SEM, EDX, AUGER and RAMAN techniques. With this new technology uniform and continuous PC-diamond films on molybdenum, Si and cemented carbides have been locally deposited onto an area of approximately 2 cm 2 with a deposition rate of up to 2 μm/min for the present. With optimisation of the process, a further significant increase in deposition rate can be expected.

The efficiency of a polycrystalline diamond coating in a DC arc-jet setup with a power of 5–10 kW was enhanced by extension of a high temperature jet core. Two approaches were investigated. First, an expansion of the plasma jet anode channel was employed. It allowed us to increase the process efficiency from 5.5 to 10 mg/h/kW by optimizing values of pressure and CH4 content in a reactionary Ar/H2/CH4 mixture. In the second approach, the extension of the hot jet core was achieved by an additional downstream discharge with a power of 2.5 kW. The secondary discharge was initiated between a positively biased auxiliary electrode and the arc-jet nozzle. This method allowed us to obtain a growth rate of 40 μm/h on an area of 12 cm2, which corresponds to an efficiency of 16 mg/h/ kW.

Simultaneous UV-laser irradiation during the deposition of DLC films has been found to significantly influence the growth process and to favourably modify the film properties. The influence of the spectral and energetic parameters of laser radiation was investigated with respect to the optical, structural and mechanical properties of DLC films. Detailed investigations on the mechanism of laser-induced structural transformations in DLC films are presented, as studied by Raman spectroscopy. Further, the characteristic peak for the nanocrystalline diamond phase at 1140 cm −1 was evident for irradiated films. Noteworthy is the increase in film microhardness with increasing energy of the deposited carbon ions with a simultaneous reduction in internal stresses, caused by photolytically induced modification of the film structure by UV-laser radiation. As a result, hard (up to 30 GPa) and thick (up to 3 μm) defect-free DLC films without cracks have been synthesized.