Effect of Carbon Fiber Orientation when Cold Spraying Metallic Powders onto Carbon Fiber-Reinforced Polymers

A previous study on the pull-off testing of metallized carbon fiber-reinforced polymers (CFRPs) via cold spray showed that better adhesion strengths could be obtained when features such as carbon fibers or surfacing elements were present, by providing potential mechanical interlocking features. In this work, a first approach to determining the effect of the fiber orientation on the deposition and bonding of the metallic coating to the thermoplastic composite substrate is explored. Pure Sn powder was cold sprayed onto two thermoplastic Polyether–Ether–Ketone (PEEK) CFRP substrates, containing carbon fibers with different orientations: one had fibers in the plane of the substrate (unidirectional tape), while the other had fibers mostly perpendicular to the substrate (ZRT film). Characterization of the coatings was performed via scanning electron microscopy (SEM) and confocal microscopy, and some aspects of mechanical testing (namely wear and scratch testing) were carried out to assess the effect of the substrate on the properties of the coatings. A slight improvement of the coating deposition was observed on the sample with the ZRT film, and this was associated with deeper penetration of tin into the substrate, around the carbon fibers, for improved mechanical interlocking. Wear testing did not seem to reveal any differences between both samples. Finally, scratch adhesion tests were performed to qualitatively assess the bonding mechanism at the coating-substrate interface, and while adhesive failure seems to be the main failure mechanism, the coating of the Z sample seems to co-deform with the substrate during testing, which could highlight better adhesion strength.