ICMCTF2005 Session G2: Scale-up, Technology Transfer and Manufacturing Aspects

In-situ doping with boron precursor gases during activated chemical vapour deposition yields conductive polycrystalline diamond coatings. To achieve low electrical resistances in the range of mOhm x cm doping levels of a few thousand ppm are required. Even for these high doping levels CVD diamond films exhibit extreme electrochemical stability together with the largest known overpotential for water electrolysis. In particular this combination of properties is the reason for increasing efforts with the aim of developing highly efficient electrochemical processes using boron-doped conductive diamond electrodes[1, 2], which represents a large scale application for CVD diamond films. Such diamond electrodes are fabricated mainly by coating conventional electrode materials like niobium or titanium. However, also other conductive substrate materials withstanding deposition conditions at temperatures between 600°C and 1000°C are also used. Major fields of application of diamond electrodes are water treatment and electrochemical synthesis. A prerequisite for this kind of application is the availability of large area electrodes. We have therefore developed a hot-filament activated CVD process with maximum diamond deposition areas of 500 mm by 1000 mm. Additionally, performance criteria like electrode lifetime and current efficiency have to be investigated. Due to the variety of volumes and contaminant load electrochemical water treatment applications also impose different requirements on electrode systems and operation parameters, including the possibility of integration into a treatment concept consisting also of conventional water treatment methods. Thus beside process and diamond electrode development also new electrochemical cells for optimization of treatment processes have been developed.

[1] New Diamond and Frontier Carbon Technology, 12 (2), 2002, Special Issue on the 4th International Workshop Diamond Electrodes

[2] New Diamond and Frontier Carbon Technology, 13 (2), 2003, Special Issue on the 5th International Workshop Diamond Electrodes

Our research into nanostructured and nanocomposite coatings led us, three years ago, to the market introduction of the revolutionary π80 coating unit. This compact industrial PVD system has since been a success story for many SMEs who require productibility, flexibility and coating performance. The π80 LAteral Rotating ARC-Cathodes (LARC^®) Technology enables, among others, the production of high performance Ti and Cr-based nanocomposite coatings. Optionally a Laser Arc Module can be attached to the chamber, allowing the user to freely combine both technologies and use the benefits of carbon-based layers.

In order to offer the user a highly productive, yet bigger platform, the new CEntral Rotating Cathode (CERC^®) concept has been integrated in our recently released equipment, the π300. This unit joins a high deposition rate, high capacity and flexibility in one compact unit. For even larger dimensions, the PL2001 Compact has been introduced. This machine is based on the proven PL1000 technology and satisfies demands for virtually any kind of large diameter substrates.

The presentation will focus on outlining the huge market potential of coatings such as nACo^®, Al_1-xTi_xN/Si₃N₄, produced on the platforms mentioned above.

Reactive sputtering in the presence of two reactive gases presents special control problems because one of the two gases may trap the target in a poisoned mode [1-2]. Recent work has shown that to avoid this trapping effect, it is necessary to control the partial pressure of each reactive gas [3]. Flow control of both gases or flow control of one gas and partial pressure control of the other gas leads to the trapping problem. To control the partial pressure for multiple reactive gases, it is necessary to provide individual feedback signals to the controller for each reactive gas present in the chamber. Cathode voltage or OES signals based on the decrease in intensity of a sputtered species wavelength will not work because they cannot distinguish which reactive gas is causing the change in the feedback signal. Sensors that will work with multiple gas reactive sputtering control systems are a mass spectrometer and an OES system that acquires optical signals from each reactive gas. There are advantages and disadvantages to each. When the length of the cathode exceeds about 50 cm, it becomes necessary to introduce the reactive gas at multiple points or zones along the length of the cathode in order to balance the reactive gas distribution. Large cathodes for glass coating can have 7 or more reactive gas inlet zones. In this talk a new reactive gas control system capable of simultaneously controlling up to 15 inlet zones along the length of the cathode in addition to three reactive gases in each zone will be described.

[1] P. Carlsson, C. Nender, H. Barankova, and S. Berg, J. Vac. Sci. Technol. A, 11(4), 1534, 1993.

[2] H. Barankova, S. Berg, P. Carlsson, and C. Nender, Thin Solid Films, 260, 181, 1995.

[3] W. D. Sproul, D. J. Christie, D. C. Carter, S. Berg, and T. Nyberg, Proc. 46th Annual SVC Technical Conference, San Francisco, CA May 3-8, 2003, pages 98-103.

Chemical vapour deposition (CVD) is the major coating technology in cemented carbide industry. Today, about 60% of all coated cemented carbides are CVD coated. There are several reasons for this: (i)CVD can produce thick and uniform coatings. (ii) CVD is still today the only deposition technique, which can economically produce high quality coatings of Al₂O₃ on an industrial scale. (iii) Functionally graded substrates have dramatically enhanced toughness of CVD coated tools. (iv)As clear from (i)-(iii) CVD coatings exhibit superior performance in their specific application areas.

Even though the majority of the published articles in the area of wear resistant coatings deal with PVD it is important to realise that CVD technology, especially with respect to Al₂O₃, has taken important steps during the last few years. For example, Al₂O₃ can today be deposited in a controlled way with respect to phase and microstructure.

This paper discusses different approaches to modify the growth of CVD Al₂O₃ with respect to phase (alpha, kappa, gamma) and microstructure (e.g. texture, grain size). The cutting performances of the Al₂O₃ phases and textures will be compared and the wear mechanisms in conventional and Ca-treated steel will be dealt with. The work demonstrates that engineering of the CVD process by tailoring one or two chemical/mechanistic steps, such as, nucleation step for α-Al₂O₃, can produce substantially enhanced coatings.

The other important aim of this paper is to demonstrate that understanding of wear mechanisms and relevant physical properties of the coating materials can be utilised to design new coating architectures with enhanced wear properties. The obtained advances are demonstrated by practical cutting tests. It is emphasised that even though most current and past commercial coatings have been empirically developed, it is clear that the development of future coatings must be based on more scientific and systematic approaches instead of trial and error.