Élaboration et étude de l'endommagement de dépôts composites obtenus par projection dynamique par gaz froid ("cold spray") : application aux contacts électriques

Abstract : Electrical contacts, for use in contactors and circuit breakers, mainly govern the lifetime of electrical devices. Silver-based metal matrix composites (MMC's) are commonly employed to set and break the electrical contact. This kind of MMC is currently produced using powder metallurgy (P/M) operations before being brazed on copper substrates. The cold gas dynamic process could be an alternative to this classical P/M route. This process is based on the acceleration of powder particles through a De Laval nozzle. Then, particles impinge on a susbtrate to form a dense and oxide-free coating. The objective of the present work is to demonstrate the feasibility of the process for achieving electrical contacts. The spraying of silver powder has been optimized before studying composite coatings. Various characterization methods such as X-ray microtomography and TEM have been used to quantify porosity and investigate into bonding mechanisms. Such investigations are necessary to provide a better knowledge on microstructure-damage relationships. Coatings have also been tested at the contact scale. For this, tensile tests were performed on samples which have been machined from thick coatings. An original laser test was developed to induce a thermomechanical load into the microstructures. The combination of these tests permitted to rank the cold-sprayed microstructures as a function of the induced damage. On the other hand, a model based on mathematical morphology concepts is proposed to simulate coating building-up. From the whole study, the principal factors which have an influence on the coating properties (powder size, grain size, ...) were identified. Consequently, several microstructures could be selected to achieve electrical contacts. Cold-sprayed contact lifetime was determined using standard industrial bench testing. Satisfactory results, i.e. which compare well with those for conventional P/M products, were exhibited.
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Submitted on : Friday, April 8, 2011 - 10:49:16 AM
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  • HAL Id : pastel-00584319, version 1

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Gilles Rolland. Élaboration et étude de l'endommagement de dépôts composites obtenus par projection dynamique par gaz froid ("cold spray") : application aux contacts électriques. Matériaux. École Nationale Supérieure des Mines de Paris, 2010. Français. ⟨NNT : 2010ENMP0015⟩. ⟨pastel-00584319⟩

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