Bonding mechanism from the impact of thermally sprayed solid particles

Power particles are mainly in solid state prior to impact on substrates from high velocity oxy-fuel (HVOF) thermal spraying. The bonding between particles and substrates is critical to ensure the quality of coating. Finite element analysis (FEA) models are developed to simulate the impingement process of solid particle impact on substrates. This numerical study examines the bonding mechanism between particles and substrates and establishes the critical particle impact parameters for bonding. Considering the morphology of particles, the shear-instability–based method is applied to all the particles, and the energy-based method is employed only for spherical particles. The particles are given the properties of widely used WC-Co powder for HVOF thermally sprayed coatings. The numerical results confirm that in the HVOF process, the kinetic energy of the particle prior to impact plays the most dominant role in particle stress localization and melting of the interfacial contact region. The critical impact parameters, such as particle velocity and temperature, are shown to be affected by the shape of particles, while higher impact velocity is required for highly nonspherical powder

La structure circulaire de Douira (Wilaya de Djelfa, Algérie) : Une origine encore énigmatique

Située à environ 400 km au sud d’Alger et à 35 km à l’est de la ville de Messaad (wilaya de Djelfa), la structure circulaire de Douïra mesure prés de 5 km de diamètre. Elle a la forme d’un cratère avec une profondeur de l’ordre de 40 à 60 m. Cette structure sub-circulaire découpe à l’emporte pièce les calcaires cénomano-turoniens qui appartiennent au domaine de la plateforme saharienne et se situe à plus de 4 km au sud de la flexure dite « accident sud Atlasique ». Une reconnaissance préliminaire sur le pourtour du cratère a permis de noter l’existence de brèches de pentes. De plus, il existe une fracturation radiale verticale notable. Il est à souligner aussi la proximité de l’accident sud-atlasique qui pourrait avoir une influence sur les structures locales d’apparence tabulaire! Par ailleurs des données aéromagnétiques ne montrent aucune anomalie importante sous la structure en question, ce qui exclut la présence d’une intrusion basique en profondeur. Cependant ces premiers éléments d’observation ne permettent pas d’avancer une origine certaine pour ce cratère. Des études détaillées de terrain sont encore nécessaire

Artificial neural network methodology: application to predict magnetic properties of nanocrystalline alloys

International audienc

Microstructure and magnetic properties of FeSiBNbCu-Al cold spray coatings

International audienceAbstract. In this paper, the FeSiBNbCu and FeSiBNbCu-Al coatings were synthesized using cold spray technique in order to produce ferromagnetic materials. Ultra-fine grain coatings are obtained using FINEMET nanostructured powders mixed with Aluminum. Various percentages of Aluminum characterized by its low hardness were taken in account. The obtaining coatings were formed of Aluminum matrix and randomly distribution of FINEMET particles. Indeed, magnetic measurements revealed a soft magnetic character for all the powders and the coatings. 25% of Al was considered as ideal to produce a homogenous coating with good soft magnetic properties