Mixed Material Feedstocks for Cold Spray Additive Manufacturing of Metal-Polymer Composites

High-performance polymers such as poly(ether ether ketone) (PEEK) are appealing for a wide variety of industrial and medical applications due to their excellent mechanical properties. However, these applications are often limited by relatively low thermal stability and conductivity compared to metals. Consequently, many methods have been developed to metalize polymers, including physical and chemical vapor deposition and thermal spray processes, but these approaches lead to issues including poor coating quality control, low deposition rate, and high cost. Thus, cold spray has become a promising alternative to rapidly and inexpensively produce polymer-metal composites, but processing problems still arise. Deposition efficiencies of metals such as copper and aluminum on PEEK, for example, often remain below 50% and come with large degrees of porosity in some cases.

One or more polymer-metal composite bond layers may serve to support the production of stronger, thicker, and more well-adhered metallic coatings. In this study, we investigate the deposition characteristics of such initial bond layers, comprised largely of PEEK with varying weight fractions of metal added, on a PEEK substrate. We approach the cold spray of the composite bond layer in three ways: firstly by spraying the powders separately but in tandem via a dual-feeder configuration, secondly by spraying a blend of the powders prepared by manual mixing, and lastly by preparing a PEEK-metal composite feedstock via cryogenic milling. Each spray was then characterized by measurements of deposition efficiency, hardness, density, and porosity. Porosity and density data allow for the calculation of the deposition efficiency of each feedstock component. Due to the larger fraction of PEEK in the feedstock, processing temperatures far below those typically seen in PEEK metallization (300-500 °C) can be used to achieve deposition.