Surface Metallization and Ceramic Deposition on Thermoplastic-Polymer and Thermosetting-Polymer Composite Via Atmospheric Plasma Spraying

A spray coating technique is an excellent method for surface metallization and ceramic deposition to widen the application fields of irreplaceable engineering polymers. In this study, Al metallization and Al₂O₃ deposition on thermoplastic-polymers (polycarbonate, polyimide) and a thermosetting-polymer composite (carbon fiber reinforced epoxy) were conducted via atmospheric plasma spray (APS). Due to the susceptibility of polymers to thermal or mechanical damage, precise process control is required. It was shown that the engineering temperature range critically determines the process window of thermoplastic-polymers. An Al₂O₃ coating can be fabricated on polymers via an Al bond coat. Like a heat sink, the Al buffer layer enables polymers to endure process heating. In low thermally resistant polycarbonate (PC), only a low plasma energy source could be applied. Additionally, vaporization induced by Al droplet contact was a clear reason of the unstable weak interface between the coating and substrate. The coatings fabricated on polyimide (PI) substrates generally showed a continuous and clean interface with a moderate adhesion property. In the case of carbon fiber reinforced epoxy (CFRP), it is believed that carbon fibers acted as a heat sink such that considerable thermal damage of CFRP was not observed and there was not delamination of the coatings. However, fracturing of carbon fibers and epoxy resin by grit-blasting (surface pre-treatment) made the surface unstable. This led to the worst adhesion characteristics between the coating and CFRP substrate. It was demonstrated that because the available temperature range and surface condition are very sensitive compared to conventional metal substrates, advanced surface pre-treatment, precise process optimization, and additional cooling are required for successful deposition.