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RESEARCH PRODUCT

Flow phenomenon of micron-sized particles during cold spray additive manufacturing: High-speed optic observation and characterization

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Abstract A high-speed laser shadowgraph observation of the particles flow during cold spraying enables a good phenomenological characterization. The particles in-flight behaviour develops a kinematics with two regimes regardless the powder nature. When leaving the nozzle, the particles form a regime of uniform jet over a certain distance along the flow direction, and then a regime of sparse jet while particles deviate in the radial direction. This dispersion increases away from the nozzle exit and exhibits thereby an event of oblique collision during an additive route process. Under such conditions, kinematic deficiency prevails since oblique collision has shown to alter the deposition efficiency, in the literature. Albeit these particles flow regimes represent a generic behaviour, there are differences in the powder’s response depending of their features that can be combined using the parameter ρ p D p . The variance ρ p D p in cold spraying is scaled through a few cases of powders (copper, aluminium, magnesium, cermet, and PEEK). The powders dispersion becomes more and more important as ρ p D p decreases from high value (large Cu powders) down to low value (case of Mg powders). However, this tendency cannot be extrapolated to lightweight powders represented by the fine PEEK powders (low ρ p D p ) which are more stable over a larger distance due to a higher sensitivity to the axial component of the gas velocity. They get unstable later in the jet since they become sensitive to the radial component of the gas velocity due to a progressive decrease of the axial gas velocity. The fine WC-Co powders adopt similar behaviour since they are lightweight as the PEEK powders due to their porous structure.