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 polymer composites (CFRPs) with thermosetting polymer as the matrix material due to substrate erosion. In a recent study, an epoxy-CFRP was 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, for the reduction of the coating process steps, a duplex metallic coating was developed on an epoxy-CFRPs by cold spray deposition of tin (Sn) to fabricate a continuous metallic interlayer, followed by Cu electrodeposition (i.e., SnCS-CuEP). The tensile adhesion bond strength and the electrical resistivity of the duplex coating were investigated. It was found that cold-sprayed Sn coating failed adhesively in the absence of the electrodeposited Cu coating. After the electrodeposition of Cu, cohesive failure of the cold-sprayed Sn coating took place. A “dissolution-deposition” mechanism has been established to explain the cohesive failure of the coldsprayed Sn coating after electrodeposition. The cohesive strength of the Sn coating is slightly higher than that of the previously fabricated three-step coating system. The electrical conductivity of the electrodeposited Cu coating was found to be 90% of bulk Cu. These results suggest that a duplex SnCS-CuEP coating can be fabricated on epoxy-CFRPs with relatively high electrical conductivity and slightly enhanced adhesion properties as compared to multilayered coatings fabricated using a three-step electroless deposition-electrodeposition-cold spray process.