The influence of particle flux density and particle size distribution in surface morphology of cold spray coatings

In this article the coupling between the Cold Gas Dynamic Spray (CS) particle flight instance just before impact and resulting surface morphology after impact of a cluster of particles are investigated with a view to understanding the complex CS process for possible optimisation for the CS fabrication process in nano thin films. This study identifies two main variables for the analysis namely particle flux density and particle size distribution and examine their influence in the structural properties of the coatings, in particular, the deposition efficiency of the cluster of particles and its applications in functional properties of the coatings. This process determines the deposition parameters that characterize the surface roughness. Given r as a radial distance from the axis of a nozzle, and R as the maximum radial distance reached by the particles, the results indicate that increasing the flux density of a cluster beyond a certain limit (yet to be identified) creates a deformation behaviour closely related to that of a single particle, however this process lowers the deposition efficiency as r approaches R; where R is the radius of the nozzle particle flux distribution radius at impact surface and r is measured from the centre axis , (where r = 0), of the impinging particle jet to towards the peripheral (where r= R). A similar characteristic on the morphology of the surfaces is observed when particles have a varying particle size: the smaller particles (and indeed any other particle sizes) that hit the target substrate at the peripheral at an angular velocity and possibly with reduced velocity from the average particle flux jet velocity, eject outward due to the oblique impact imposed by the traverse velocity component. These findings have potential applications in fabrication of functional surfaces for various applications and provide us with control variables necessary for modifying the surfaces.