The Interaction of Surface Engineering and High Temperature Corrosion Protection

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Fibre strength selection and the mechanical resistance of fibre-reinforced metal matrix composites

For predicting the strength of fibre-reinforced metal matrix composites, the in situ fibre strength value has to be introduced in the calculations. Tension tests series have been conducted on SiC fibres (SCSO and SCS2 TEXTRON) before and after chemical interaction with a pure liquid aluminium bath and the reacted fibres have been tested before and after dissolution of the aluminium coating simulating the metallic matrix around the fibres. The results obtained for the different fibre batches show that the in situ fibre resistance may differ significantly from the strength of as-received or extracted fibres that is usually adopted in the models

ANALYSE D' INCLUSIONS D'OXYDES RESPONSABLES DE DÉFAUTS DE SURFACE INTERNE APPARAISSANT AU COURS DE LA FABRICATION DE TUBES SANS SOUDURE

Des analyses à la microsonde électronique et des observations au microscope électronique à balayage ont permis d'identifier les inclusions d'oxydes responsables de défauts de surface interne dans la fabrication de tubes sans soudure, et de proposer un mécanisme de formation de ces défauts.Based on EPMA analysis and S.E.M. observations of oxide inclusions, a mechanism is proposed for the formation of interna1 defects in seamless tube

Influence de la pression sur la conductivité thermique de barrières thermiques

Les revêtements de zircone yttriée déposés par projection plasma sont utilisés comme barrières thermiques pour protéger des pièces des moteurs aéronautiques, en particulier les parois de chambres de combustion. La diffusivité thermique d'un tel matériau a été déterminée, à température ambiante et pour des pressions allant de 10 à 105 Pa, par la méthode laser-flash (laser CO2, λ = 10,6 µm). Les variations en fonction de la pression de la conductivité thermique peuvent être décrites par un modèle simple tenant compte du fait que la conductivité thermique du gaz contenu dans les microfissures est une fonction de la pression et de leurs dimensions. Ces résultats permettent de décrire l'influence d'un traitement thermique et montrent que la valeur de la conductivité thermique dans les conditions d'utilisation peut être significativement plus élevée que celle déterminée à basse pression ou même à pression ambiante

LPCVD Pyrocarbon Coating on Unidirectional Carbon Fiber Yarns : an Efficient Interphase for Aluminium Matrix Composites

In order to optimize the interfaces in carbon fiber (high resistance Toray T800) reinforced aluminium matrix composites, a pyrolytic carbon (Cp) layer has been developed by a CVD process using a hot wall reactor operating at reduced pressure. The Cp, which has a weak shear strength, is introduced to promote adequate debonding at the fiber/matrix interface. In a first step, classical CVD studies are conducted on planar carbon substrates with a parametric investigation of the effects of temperature, pressure, reactant flow rates on the growth rate and morphology of the coating. For Cp, obtained form thermal decomposition of ethylene, a very high activation energy (310 kJ/mol) and a decrease in coating growth rate with the reactant residence time indicate that the reaction limiting step occurs in the gaseous phase. The carbon coatings exhibit a macroscopic stratified morphology which could promote internal delamination. In a second step, deposition parameters have been optimized to ensure a good infiltration of 6000 filaments yarns. Finally, the influence of carbon underlayer on the mechanical properties of coated fibers is determined by tensile tests on monofilaments and interpreted in terms of Weibull distribution. The results on aluminium composites confirm the beneficial role of mechanical fuse played by the Cp coating

Determination of mechanical properties of bondcoat materials by high temperature instrumented indentation

The integrity of thermal barrier coating systems is strongly influenced by the mechanical properties of the different layers constituting them, in particular the intermetallic bondcoats. At high temperature, interdiffusion and oxidation phenomena cause change in the composition of the bondcoats and as a result their mechanical behaviour is likely to change also. Thus the knowledge of the mechanical behaviour of bondcoats is necessary to describe the stress field present in thermal barrier systems. To determine the mechanical behaviour of alloys, such as beta-(Ni, Pt)Al in bulk form and as bondcoats, a high temperature instrumented indenter capable of functionning up to 1000 °C is used. The technique is original and enables to investigate a large number of compositions and conditions within a reasonable time. From the experiments data, the mechanical behaviour of these materials is identified, as a function of the metallurgical evolution with temperature of bondcoats alloys. The results are discussed in relation to the mechanical properties obtained by other techniques