Cold spray can substitute for several coating processes for various applications, due to a high efficiency coupled with high properties for the sprayed product. The use of a composite powder rather than a powder blend was shown to be beneficial, especially for the cold spray of electrical contacts. The objective of this work is to optimize a composite powder (Ag-14wt% SnO 2 ) using numerical simulation of the deformation of the particle at the impact onto the substrate (Cu). Every elementary composite particle was made of an agglomerate of Ag and SnO 2 smaller particles, which exhibited more or less porosity depending on the powder processing conditions. The first step was to study the distribution of these various constituting phases plus porosity. Three types of powders which showed different phases and porosity characteristics deliberately were developed. Three-dimensional images of the agglomerate were acquired using microtomography which exhibited the porosity network well in the dual-phased particle material. These actual 3D images were used to feed a simulation of the impingement of a particulate agglomerate to result in a splat onto the substrate. For this, a two dimensional deformation model was developed on the route to a three-dimensional model which is expected to be more powerful. The influence of agglomerate characteristics, primarily porosity, on the deformation behavior was studied. Consequences on splat-substrate adhesion and deposition efficiency could therefore be investigated in the light of direct observation of the cold-sprayed material.

In the present work, TiO 2 (rutile)-2.5vol.%Ag composite powders produced by mechanical milling were detonation sprayed under different atmospheres using acytelene as a fuel. The atmosphere of spraying was set to be reducing or oxidizing by changing the O 2 /C 2 H 2 mole ratio. Reduction of TiO 2 to Ti 3 O 5 occurred in the coatings deposited under a reducing atmosphere (O 2 /C 2 H 2 =1.05) when particles were heated to reach a molten or a semi-molten state. In the coatings sprayed using a stoichiometric O 2 /C 2 H 2 =2.5 mixture, the major phase was rutile. The composition of the atmosphere does not only determine the chemical environment for the sprayed powders, but also influences the temperature conditions. Increasing oxygen content in the explosive mixture led to much higher temperatures of the sprayed particles as was calculated using a previously elaborated model. When titanium dioxide did not reach melting, the coatings were porous with a spongy surface. Coatings formed by fully or partially molten particles possessed a denser structure. Silver particles experienced melting during spraying but remained uniformly distributed in the coatings. This study demonstrated that careful selection of the composition of the spraying atmosphere offers potential of controlling the phase composition and microstructure of the detonation sprayed coatings.

A direct write method of fabricating antenna structures onto doubly curved dielectric surfaces has been developed using low temperature kinetic metallization. This paper describes the process and its use for depositing copper on various dielectrics and silver on alumina substrates and copper lead frames.

In this work, the microstructure of silver coatings obtained by cold spraying with a fine and a rather coarse powder were investigated. Cold-sprayed microstructures strongly depend on the deposition process parameters. These parameters have an influence on porosity, plastic strain, particle-to-particle bonding mechanisms. The originality of this study rests on the use of X-ray microtomography, which is shown to be a very powerful technique to investigate into cold-sprayed coatings. Several samples were machined from coatings by electro-discharge machining (EDM) then scanned using microtomography. Porosity fraction was determined by three-dimensional image analysis and compared to classical two-dimensional analysis of micrographs. A difference between the two methods was exhibited, which showed sample preparation effects. Consequently, X-ray microtomography seems to be well adapted to study cold-sprayed coatings thoroughly. Another result from this work was the characterization of the morphology of pores and deformed particles. Bonding mechanisms in cold spray could therefore be discussed. In addition, the knowledge on deformed particles allowed to simulate cold-sprayed coatings with build-up models. This will be done in a further work