Multi-Purpose Additives Towards a Better Polymer Cold Spray Process

Polymers have proven to be challenging to cold spray, particularly with high efficiency and quality in inexpensive nitrogen (N₂) and air gasses. Helium as a process gas has been used to improve spray properties, but is undesirable due to its limited availability and high cost. In this study, additives of multiple particle sizes and materials were mixed with polymer powder in an effort to improve the performance of polymer sprays using N₂ as a process gas. Hard-phase additives demonstrated nozzle-cleaning properties that continually remove polymer fouling on the nozzle walls. Conversely, sprays with polymer powder and no additives tended to clog the nozzle throat and diverging section as a result of continual fouling. The effects of additives on deposit microstructure were investigated by precise ion-beam polishing of deposit cross sections, and subsequently imaging with an electron microscope. Additional metrics including the density and post-spray composition of deposits were investigated as a function of the additive used.