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JUNE 28 WEDNESDAY AFTERNOON JS2-WeA-P.8 NANO TO MICROMETRIC HFCVD DIAMOND ADHESION STRENGTH TO Si 3 N 4 . F.A. Almeida, M.S. Amaral, F.J. Oliveira, R.F. Silva. Dept. of Ceramics and Glass Engineering, CICECO, Univ. of Aveiro, 3810-193 Aveiro, Portugal. A.J.S. Fernandes. Dept. of Physics, Univ. of Aveiro, 3810-193 Aveiro, Portugal CVD diamond coated materials possess unique properties (hardness, thermal conductivity, chemical inertness) that demand their selection as components of tribosystems working under mechanical and/or chemical severe conditions. Examples of such applications are cutting tools for highly abrasive materials and mechanical seals for pumping of corrosive liquids. Furthermore, an increasing interesting field of application is biomedicine, namely cirurgical tools and coatings for articular implants, where diamond’s biocompatibility is an essential issue. However, the high surface roughness of conventional microcrystalline CVD diamond is a major problem when considering such purposes, as the sliding contact of diamond asperities may increase stress and temperature levels, leading to an increasing wear rate. To overcome this drawback, today’s goal is the development of diamond crystals with very small grains of nanometric size by adequate CVD parameters, avoiding the typical columnar growth of microcrystalline diamond structures. When considering tribological and mechanical applications, adhesion of the film to the substrate determines the success of the component in service. In this study, distinct diamond coatings on silicon nitride ceramic substrates with different crystallite sizes were investigated: i) nanocrystalline diamond (~25 nm); ii) submicrometric diamond (~ 40 nm); and iii) conventional micrometric size (~10 μm). The coatings, with thickness of about 40 μm, were grown by hot filament CVD technique. The effect of these diamond structures on adhesion strength to the ceramic substrate will be evaluated by Brale tip indentation and correlated with their Raman signature. 140
JUNE 28 WEDNESDAY AFTERNOON JS2-WeA-P.7 STUDY OF SOME PROPERTIES OF HARD TUNGSTEN CARBIDE COATINGS. F. Khalfallah, Y. Hadjar, R. Halimi. Laboratoire des Couches Minces et Interfaces, Département de Physique, Faculté des Sciences, Université Mentouri, 25000 Constantine, Algérie. In this work, we have studied the properties of hard coatings of tungsten carbides. The samples are thin layers of Tungsten deposited at 500°C on two types of steel (containing 1 and 0,7% wt. carbon) substrates. The samples were then heat treated in vacuum, at various temperatures (500-1000°C) and during different times. The formation of tungsten carbides, the evolution of the microstructure and the morphology of the surface of samples were followed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The measurements of micro-hardness were carried out by Vickers tests. Thermal annealing produces reactions and some other structural changes in the tungsten layers which depend on the carbon content in substrate. It is established that the formation of tungsten carbides occurs above annealing at 800°C. The reaction is more rapid on substrate containing 1%C. The mono-carbide WC forms after annealing at 1000°C. The hardness of coatings increases continuously from 400 to 1200 Kg/mm² as the temperature of annealing increases from 500 to 900°C. The samples rich on carbon show higher hardness. Key words: hard coatings, tungsten, carbides, thin films. Presenting author: F. KHALFALLAH Contacts and email: Tel/Fax: 213 31 61 47 11; fa_fares@yahoo.fr Presentation type: Poster 139
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Sigilum Universitatis Studii Salama
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