Powder stream characteristics in cold spray nozzles

Abstract

The exponential increase of industrial demand in the past two decades has led scientists to the development of alternative technologies for the fast manufacturing of engineering components, aside from standard and time consuming techniques such as casting or forging. Cold Spray (C S ) is a newly developed manufacturing technique, based upon the deposition of metal powder on a substrate due to high energy particles impacts. In this process, the powder is accelerated up to considerable speed in a converging - di verging nozzle, typically using air, nitrogen or helium as a carrier gas. Recent developments have demonstrated significant process capabilities, from the building of mould - free 3D shapes made of various metals, to low porosity and corrosion resistant tita nium coatings. In the C S process, the particle stream characteristics during the acceleration process is important in relation to the final geometry of the coating. Experimental studies have shown the tendency of particles to spread over the nozzle acceler ation channel, resulting in a wide exit stream and in the difficulty of producing narrow tracks. This paper presents an investigation on the powde r stream characteristics in C S supersonic nozzles. The powder insertion location was varied within the carrier gas flow, along with the geometry of the powder injector , in order to identify their relation 2 with particles trajectories. Computational Fluid Dynamic (CFD) results by Fluent v6.3.26 are presented, alo ng with experimental observations . Different configurations were tested and modelled, giving deposited track geometries of copper and tin r anging from 1mm to 8mm in width on metal and polymer substrates.