Modélisation de la section de dépôts obtenus par fusion d'une poudre métallique projetée dans un faisceau laser Nd-YAG

This work presents a cross-section modeling of laser claddings by powder spraying in a cw Nd-YAG laser. We admit a homogeneous temperature repartition inside each powder particle during interaction time, a material's intern energy variation equals its absorbed energy and an optical extinction through a powder cloud following a Beer-Lambert law. Apart the good correlation obtained between model and experiments, this one shows experimentals data which change widely the cross-section (power, power feed, scanning speed). And we define and obtain experimentally an absorption coefficient which is nearly the value of a liquid metal absorption coefficient.L'objectif de cette étude est la modélisation de la section des dépôts obtenus lors d'opération de revêtement de surface par projection de poudre dans un faisceau laser Nd-YAG. Pour ce faire, nous admettons que la répartition des températures au sein de chaque particule est homogène pendant le temps d'interaction, que la variation d'énergie interne du matériau est égale à l'énergie absorbée par celui-ci et que l'atténuation du faisceau au travers du nuage de poudre suit une loi de type Beer-Lambert. Outre la bonne corrélation obtenue entre le modèle et l'experience, les paramètres opérationnels qui influent fortement sur le résultat apparaissent clairement (puissance, débit de poudre, vitesse de travail). Enfin, nous définissons et obtenons expérimentalement un coefficient d'absorption qui est de l'ordre de grandeur du coefficient d'absorption d'un métal en phase liquide

Qualification and Post-Mortem Characterization of Tungsten Mock-ups Exposed to Cyclic High Heat Flux Loading

In order to evaluate the option to start the ITER operation with a full tungsten (W) divertor, high heat flux tests were performed in the electron beam facility FE200, Le Creusot, France. Thereby, in total eight small-scale and three medium-scale monoblock mock-ups produced with different manufacturing technologies and different tungsten grades were exposed to cyclic steady state heat loads. The applied power density ranges from 10 to 20 MW/m2 with a maximum of 1000 cycles at each particular loading step. Finally, on a reduced number of tiles, critical heat flux tests in the range of 30 MW/m2 were performed.Besides macroscopic and microscopic images of the loaded surface areas, detailed metallographic analyses were performed in order to characterize the occurring damages, i.e., crack formation, recrystallization, and melting. Thereby, the different joining technologies, i.e., hot radial pressing (HRP) vs. hot isostatic pressing (HIP) of tungsten to the Cu-based cooling tube, were qualified showing a higher stability and reproducibility of the HIP technology also as repair technology. Finally, the material response at the loaded top surface was found to be depending on the material grade, microstructural orientation, and recrystallization state of the material. These damages might be triggered by the application of thermal shock loads during electron beam surface scanning and not by the steady state heat load only. However, the superposition of thermal fatigue loads and thermal shocks as also expected during ELMs in ITER gives a first impression of the possible severe material degradation at the surface during operational scenarios at the divertor strike point