Towards the Industrialization of Superhard Nanocrystalline Composites for High Speed and Dry Machining
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TOWARDS THE INDUSTRIALIZATION OF SUPERHARD NANOCRYSTALLINE COMPOSITES FOR HIGH SPEED AND DRY MACHINING Mojmir Jileka, Pavel Holubara, Maritza G. J. Veprek-Heijmanb, Stan Veprekb,*); aSHM Ltd. CZ-78803 Novy Malin 266, Czech Republic, e-mail: [email protected]; bInstitute for Chemistry of Inorganic Materials, Technical University Munich, Lichtenberstr. 4, D-85747 Garching b. Munich, Germany, e-mail: [email protected]; *) Corresponding author ABSTRACT Novel superhard wear resistant nanocomposite coatings nc-(Ti1-xAlx)N/a-Si3N4 for advanced machining tools were developed and introduced into large scale industrial production within a relatively short time. We describe the development of the coating technology based on vacuum arc evaporation from a specially designed cylindrical cathode and, as a result of that development, the improvement of the properties and machining performance of the coatings. ITRODUCTION The demand on the improvement of machining technology in terms of higher cutting speed, better quality of the machined surface, lower consumption of lubricants and coolants calls for the development of new wear resistant coatings for machining tools. Because the costs of environmentally friendly recycling and disposal of the coolants represents a significant part of the total machining costs, the ultimate goal is dry, fast machining. Under such conditions, the temperature of the cutting tool and of the coatings can reach 800°C or more. This poses strong requirements on the quality of the coatings, such as a high hardness combined with a high resistance against crack formation and adherence to the substrate, high temperature stability and oxidation resistance, low coefficient of friction, absence of reaction with the material being machined and others. For these reasons, the earlier developed (Ti1-xAlx)N [1] [2] and (Ti1-xAlxYy)N coatings [3] [4] are progressively replacing TiN because of their significantly higher oxidation resistance (for lack of available space we don’t discuss here other dedicated coatings, such as heterostructures, self-lubricant hard coatings, low friction coatings for bearings and others). In the present paper we shall show that the recently developed superhard nanocomposites, which are formed according to the generic design principle [5] [6] by self-organisation due to thermodynamically driven spinodal phase segregation, meet the requirements for a new generation of advanced wear resistant and tribological coatings. The SHM was established in 1993 as a small company producing a variety of specialised products, such as a special coating for spark plugs which enables a more uniform ignition of the gasoline-air mixture in the engine, diamond dressers and others. In 1994 the development of the nc-(Ti1-xAlx)N/a-Si3N4 begun motivated by the work of Li Shizhi et al. [7]. Later on, when the generic principle for the design of the nanocomposites was published by Veprek et al. [5], a collaboration between SHM and the Technical University of Munich begun. In 1996 the first coatings on indexable inse
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