Development of a Duplex Sn-Cu Coating on Carbon Fiber-Reinforced Polymers (CFRPs) using Cold Spray and Electrodeposition Processes

Direct cold spray deposition of Cu was not possible on carbon fiber-reinforced polymers (CFRPs) due to substrate erosion. In a recent study, epoxy-CFRPs were successfully metallized through a hybrid coating process that involves three consecutive coating steps: (i) electroless deposition, followed by (ii) electrodeposition, and finally (iii) cold spray. In this present study, to reduce the number of coating steps, a duplex metallic coating was developed on CFRPs by cold spray deposition of tin (Sn) followed by Cu electrodeposition (Sn_cs-Cu_ep). Copper was selected for electrodeposition due to its superior electrical conductivity, which makes it suitable as a lightning strike protection coating material. The pull-off strength of the duplex coating was measured in accordance with ASTM Standard C-633-13. Fractured surfaces after pull-off testing were examined using a scanning electron microscope (SEM) and an optical microscope (OM). The electrical resistivity of the fabricated coatings was evaluated using the 4-point probe method. A “dissolution-deposition” mechanism has been established to explain the adhesion/cohesion behavior of the cold-sprayed Sn coating after electrodeposition. The results suggest that a duplex Sn_cs-Cu_ep coating can be fabricated on CFRPs with significantly improved electrical conductivity and slightly enhanced adhesion properties compared to the previously fabricated three-step coating system.