Adhesion strength improvement of thermally sprayed metallic coating on carbon-fiber-reinforced polymer composite

Surface metallization of carbon-fiber-reinforced polymer (CFRP) composites using thermal spray has emerged as a promising approach to enhance their thermal and electrical properties for high temperature applications. However, poor adhesion between the metallic coating and the CFRP substrate remains a critical challenge. This article examines the current state of research on improving the adhesion strength of thermally sprayed coatings on CFRP substrates. Zn and yttrium-aluminum-garnet (YAG) bond coatings were applied on a thermosetting-based epoxy-CFRP substrate, respectively, using wire arc spray and plasma spray (PS) techniques. Cr₂O₃ and Cr₂O₃-Al₂O₃ top coatings were subsequently plasma sprayed on Zn and YAG bond coatings, respectively. Adhesion strengths of the bond coatings were determined by conducting pull-off adhesion tests; the YAG bond coating demonstrated superior adhesion strength compared to the Zn bond coating. Scanning electron microscope and electron probe micro-analyzer were employed to characterize interfaces of the bond coatings and CFRP substrate, as well as the peeled CFRP surfaces. The obtained results of this study revealed that high-temperature YAG particles melted by the extremely high plasma temperature employed in the PS process, induced transient delamination of the substrate's surface epoxy layer, thereby exposing the underlying carbon fibers (CFs). The enhanced adhesion strength of the YAG bond coating was attributed to two key effects: (1) direct interaction between exposed CFs and incoming YAG particles, suggesting mechanical interlocking, and (2) partial penetration of lifted CFs into the solidified YAG coating layer.