Obtention d'alliages réfractaires SiCxNy(O) par dépôt chimique à oartir d'une gazeuse Si(CH3)4-NH3

By pure thermal CVD from Si(CH/sub 3/)/sub 4/NH/sub 3/ mixtures SiC/sub x/N/sub y/(O) films have been prepared at 1475 K. Using electron microprobe analysis a continuous composition variation between SiC and Si/sub 3/N/sub 4/ is shown. The difficulty of quantitative analysis due to the conductivity of the samples is underlined. By selecting the right conditions, precise measurements were obtained. These films have an optical energy band gap in the range 2.2-4.1 eV and a constant photoluminescence peak. The film structure is discussed and these materials may be probably ascribed to an alloy phas

Errata — Possibilités de stockage de l'énergie solaire à partir de sulfates

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ADHERENCE AND PROPERTIES OF SILICON CARBIDE BASED FILMS ON STEEL

Coatings of silicon carbide with various compositions have been obtained in a r.f plasma assisted process using tetramethylsilane and argon as input gases. Some properties against mechanical applications of such deposits on steel have been investigated. Residual stresses and hardness are reported and discussed in relation with plasma parameters and deposit composition. By scratch testing, it was shown that the silicon carbide films on steel denote a good adherence when compared with previous data encoutered in the litterature for titanium carbide or nitride deposits though low critical load values. Adherence is discussed in relation to the nature of the interfacial zone examined hy Auger depth profiling. It is conclude that the films have promising variable properties which can be optimized by acting on plasma parameters

KINETIC APPROACH OF THE DEPOSITION OF SILICON CARBIDE BASED FILMS OBTAINED BY PACVD

Silicon carbide deposition in an inductively coupled RF plasma reactor using tetramethysilane(TMS)/argon mixtures was carried out on steel substrates in a restricted range of experimental parameters. A kinetic approach in the pressure range of 0.7-2.4 kPa is made to correlate the deposition rate of silicon carbide with plasma parameters. A "global" or "effective" concept has been emphasized. The main contribution of TMS dissociation in the present pressure range is assumed to the excited Ar(ion and metastable atom)-TMS molecule reactions rather than the primary electron-TMS reactions. A simple analytical expression for deposition rate is deduced which provides a good fit with experiments

SiCN coatings prepared by PACVD from TMS-NH3-Ar system on steel

SiCN coatings with continuous composition between Si3N4 and Sic (rich in Si) have been prepared by acting on the tetramethylsilane (TMS)/ammonia ratio in the gas phase. The deposit compositions (10 μm thick films) have been investigated by different means which stress the difficulties encountered. Nevertheless the trends are in fair agreement. An increase in ammonia partial pressure favors the incorporation of N in the deposits. XPS studies of the samples lead to the conclusion that the chemical environments of Si, C, N are more complicated than in a mixture situation ; there would be various bonding States. Deposition rates range from 12 μm h-1 up to 30 μm h-1 and are largely increased when dilution is reduced. Hardness and Young's modulus are driven by the C/N ratio : HV lies between 22.6 GPa (Si3N4) to 26.2 GPa (SiC) with respectively apparent Young's modulus from 250-295 up to 357-431. All the films exhibit an adhesion of same order though N tends to increase the critical loads

THERMODYNAMIC CALCULATION OF THE TWO PHASED DEPOSITION DOMAINS WITH SiC IN THE Si-Ti-C-Cl-H CHEMICAL SYSTEM

Dans le système Si-Ti-C, les nouveaux matériaux dispersoïdes à base de carbure de silicium suscitent un vif intérêt dans la recherche de l'amélioration de la ténacité. L'étude thermodynamique du système chimique complexe Si-Ti-C-Cl-H a permis de représenter les domaines de dépôt des équilibres biphasés SiC-TiC et SiC-Ti3SiC2 dans le repère des paramètres de variance. Pour une composition donnée de la phase gazeuse à l'équilibre, la composition de la phase condensée peut varier dans des proportions importantes en fonction du mélange gazeux initial. A partir de cette unique représentation, les domaines de depôt sont déduits pour un mélange gazeux initial quelconque.New ceramic materials with dispersed phases within a silicium carbide matrix in the Ti-Si-C chemical system seem very attractive to improve toughness properties. Deposition domains of SiC-TiC and SiC-Ti3SiC2 are determined by thermodynamic calculation in the Si-Ti-C-Cl-H chemical complex system, and presented in the coordinate system of the variance parameters. The representation of these domains in the coordinate system of the initial gas mixture is then easily deduced whatever the bearing molecule considered. For a given composition of the gas mixture at equilibrium the ratio between the deposited phases can present very large variations according to the initial gas-mixture

TITANIUM CARBIDE COATINGS ON STEEL : STUDY OF THE CONDITIONS OF ELABORATION AND OF SUBSTRATE-COATING INTERACTIONS

La méthodologie des plans d'expérience a été appliquée au dépôt de TIC sur des aciers hypoeutectoïdes faiblement alliés. Des modèles descriptifs de l'épaisseur du revêtement et de la variation de poids ont été obtenus et corrélés à des calculs thermodynamiques dans le domaine expérimental envisagé. Les surfaces de réponse correspondantes ont été utilisées pour étudier quelques propriétés. Il a été observé que pour une épaisseur constante, le coefficient de frottement du couple TiC/acier varie fortement avec la morphologie qui est fonction du mécanisme de dépôt. Les valeurs élevées des microduretés sont attribuées à un effet de taille de grains. Les contraintes résiduelles ont été évaluées. Il a été montré que la décarburation du substrat dans les conditions généralement utilisées ne peut être complétement évitée.The methodology of experimental designs was applied to the deposition of TiC on weakly alloyed hypoeutectoïd steels. Models describing the coating thickness and weight change were obtained and correlated with thermodynamic calculations. The corresponding response surfaces were used to study some properties of the deposits. The friction coefficient of a titanium carbide/steel couple has been observed to present a particularly large variation with respect to the surface morphology, which depends on the experimental conditions. The highvalues of microhardness wich were measured were presumed to be induced by a grain size effect. The residual stresses wre evaluated. It has also been shown that substrate decarburization cannot be completely avoided with the usual coating conditions used by previous authors