Thermoplastic coating on fiber reinforced polymer composites by cold spray additive manufacturing

This work investigates the cold spray coating of nylon 6 on fiber-reinforced composite substrates. Deposition conditions are investigated by systematically varying the process parameters (impact velocity, temperature, carrier gas pressure, and flow rate) for two woven fiber-reinforced epoxy substrates with glass and carbon fiber reinforcements, resulting in deposition efficiencies exceeding 30%. Parametric studies are performed to identify the optimal system pressure and powder flow rates that lead to the successful deposition of the powder particles on composite substrates. It is observed that, upon impact, the particles undergo extensive plastic deformation without damaging the reinforcing fibers in the substrate. Microstructural observations reveal that the first (seeding) layer of nylon particles experiences a higher degree of plastic deformation due to the impact on a stiff substrate. The large plastic deformation in the impacting particles plays a key role in enabling adhesion to the substrate. The successive layers of deposited particles undergo less plastic deformation as they impact a comparatively softer pre-deposited nylon substrate. The underlying deposition mechanisms are further explored using multiscale finite element analyses. Results obtained in this work demonstrate the feasibility of cold spray deposition of thermoplastic particles on fiber-reinforced composites without imposing significant damage to the substrate.