Peening Effect of Glass Beads in the Cold Spray Deposition of Polymeric Powders

Abstract

Cold spray is a green additive manufacturing method that accelerates micron-size particles to supersonic speeds. At these high speeds, the particles deposit upon impact with a desired surface. High-density polyethylene, polyurethane, polyamide-12, polystyrene, and ultra-high molecular weight polyethylene particles were cold-sprayed onto a low-density polyethylene substrate under different process conditions. Glass beads with diameters between 20 and 120 µm were added to each batch to study the effect of non-adhesive peening particles on the deposition efficiency and the quality of the final deposited layer of a series different polymeric powders. The successful deposition window was compared for the cold spray process with and without the addition of glass beads. Adding the glass beads to the polymer powders was found to widen the successful windows of deposition to both higher and lower impact velocities at a given temperature for all the polymer powder studied. In addition, adding peening particles were found to make deposition possible at lower particle temperatures where deposition had not been successful previously. This was especially important for ultra-high molecular weight polyethylene particles for which deposition in the absence of peening particles was not possible below 60 °C, but with peening particles was successful even at room temperature. Peening particles were found to increase deposition efficiency by as much as 50% for a given set of deposition conditions. The appropriate size of the added glass beads to maximize the deposition efficiency was found to be comparable to the size of the depositing particles. The addition of glass beads was also found to reduce the surface roughness of the deposited layer by more than 50%. Finally, for processing conditions with particle velocities below a Mach number of one, no glass beads were found to adhere to the resulting cold-sprayed substrates.