Tribological Properties of Superhard PVD Coatings
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TRIBOLOGICAL PROPERTIES OF SUPERHARD PVD COATINGS 0. Knotek, F. L6ffler University of Technology, IWKB, Templergraben 55, W-5 100 Aachen, Germany
Abstract In order to advance the development of extremely hard coatings, new homogeneous and metastable films were prepared by magnetron sputter ion plating (MSIP) and arc ion plating (AIP) in the DC. or RF. mode. In the present study coatings in the systems Ti-B-C-N, SI-C-N and amorphous carbon coatings (ADLC) were investigated and compared with other hard coatings. Multicomponent layers of different compositions and structures were deposited by varying the reactive gases methane (CH 4 ) and nitrogen (N2 ) and the dominant process parameters (e. g. C/V-characteristic of the cathode, substrate bias). X-ray diffraction studies of the Ti-B-C-N coatings revealed either an amorphous structure or crystallization in a hexagonal lattice. The ADLC and Si-C-N coatings were always amorphous. Electron microprobe analysis and auger electron spectroscopy were used to determine the coating compositions. The tribological properties were determined by a ball on disc tribometer (e.g. friction coefficent), a pin on disc tribometer and a special abrasive wear test.
Introduction The coating of indexable tips for steel machining applications has already led to a substantial lengthening of tool lives. This proved particularly advantageous in the context of increasingly atomated industrial production, where longer tool lives achieved a considerable reduction in non-productive machine times. Today, machining relies almost exclusively on coated cemented carbides. which combine higher wear resistance with the ability to work under extreme cutting parameters. At the same time the demand for superhard coatings like TI-B-C or SiC increases continiously. To obtain optimum results for a specialized application, suitable parameter combinations have to be found. Development is made more difficult by the fact that a change in one area may affect other main influencing variables (e.g. an insulating substrate alters the electrical field in the process). The result may be a modification of the process. Mat. Res. Soc. Symp. Proc. Vol. 239. 01992 Materials Research Society
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PVD Coating Processes The reactive variants of the magnetron-sputtering ion-plating (MSIP) and arc ion-plating (AiP) processes are of primary interest for the deposition of tribological films. They possess a number of advantages as compared to CVD processes. The PVD principle possesses enormous flexibility in terms of the choice of coating and substrate materials, allowing cost-effective small-batch production of different coating composites. Substrate temperatures can also be set as low as desired, enabling even plastics to be coated. The process is also environmentally compatible, since, unlike CVD, it does not entail disposal of large quantities of aggressive process chemicals. Fig. I compares the two above-mentioned PVD processes / I/. The main difference lies in the method by which the vaporized metal particles are produced. In
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