Properties of Multilayered Metallic Coatings Deposited on Carbon Fiber-Reinforced Polymers (CFRPs) through Electrochemical and Cold Spray Processes

Previous studies have shown that copper (Cu) may be cold spray deposited on epoxy carbon fiber-reinforced polymers (CFRPs) if an interlayer Cu of electroplated on an electroless nickel (Ni) coating is present prior to cold spraying. In this present study, the tensile adhesion bond strength of these multilayered metallic coatings was measured in accordance with ASTM Standard C-633-13. Fractured surfaces after tensile adhesion testing were examined by scanning electron microscopy (SEM) and optical microscopy (OM). Scratch adhesion testing from the polished cross sections of the multilayered coatings was also performed to compare the results with those obtained from the tensile adhesion testing. The microstructure of the cold-sprayed and electroplated Cu coatings was analyzed by electron channeling contrast imaging (ECCI), and its correlation with hardness values was studied. Adhesive failure at the Ni coating/CFRP interface was observed in the absence of a cold-sprayed Cu coating. Enhanced bonding between electroless Ni coating and exposed carbon fiber areas was observed relative to the epoxy regions. This enhanced bonding was attributed to the increased roughness of the carbon fiber regions relative to the epoxy areas. However, after cold spraying with Cu, cohesive failure of the cold-sprayed Cu coating occurred, which was likely due to insufficient plastic deformation of the particles cold sprayed close to the critical velocity of Cu. Electron channeling contrast imaging analysis from the cross sections revealed uniform and inhomogeneous microstructures within the electroplated and cold-sprayed Cu coatings, respectively.