Development of hybrid metallic coatings on carbon fiber-reinforced polymers (CFRPs) by cold spray deposition of copper-assisted copper electroplating process

Abstract

Metallization of polymeric materials such as carbon fiber-reinforced polymers (CFRPs) by the cold spray technique has gained significant interest to enhance their electrical conductivity. Copper is a very good electrical conductor, which makes it favorable for applications that require high electrical conductivity. However, previous studies showed that continuous copper coatings could not be fabricated directly on CFRPs by cold spraying. In this study, a hybrid fabrication process was used to enable cold spray deposition of copper onto CFRPs, making them electrically conductive. The CFRP substrate was first metallized with an electroless Ni coating; subsequently, a thick copper layer was electroplated onto the Ni interlayer. Copper was then cold spray deposited onto the electroplated CFRP as well as on a Cu control panel. Deposition efficiency (DE) of the cold-sprayed coatings was measured for both the CFRP and the control Cu coupons to determine optimal deposition conditions. Surface and cross-sectional morphologies of the coated CFRP were investigated, and both the electroplated CFRP and control panels were characterized for mechanical properties and surface roughness before cold spray deposition. The electrical resistivity of the cold-sprayed CFRPs was evaluated. It was found that the DE of copper particles is sensitive to the surface characteristics of the substrate. The electrical resistivity of the cold-sprayed coatings was slightly higher than that of the bulk copper due to porosity and small defects on the coating surface. The results suggest that Cu coatings can be successfully fabricated onto CFRPs if a copper inter-layer is present. This layer not only protects the CFRP from any possible damage, but also improves the cold sprayability of copper particles as compared to the conventional cold spraying copper powder/copper panel due to its favorable mechanical, thermal and surface properties. The fabricated coatings can serve as conductive surfaces for application as lightning strike protection coatings.