November/December AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 8 3 8 iTSSe TSS iTSSe TSS T here is increasing interest in polymer coatings on me- tallic substrates and metallic coatings on polymer substrates for use in various applications. For the for- mer, Impact Innovations focused on the application of poly- etheretherketone (PEEK) on metallic surfaces because the properties of thehigh-performancepolymer areadvantageous in medical, tribological, and insulation applications to name a few. The biocompatibility of PEEK makes it a good candidate for orthopedic implants and medical instruments [1] . Tribolog- ical applications include use as bearing and sliding material due to good friction and wear resistance [2, 3] , and its thermal stability makes it useful for cable and wire insulation [4] . PEEK has been produced in the formof plates by compressionmold- ing [5] and hot pressing [6] . PEEK coatings on metallic substrates have been pro- duced using high-velocity oxy fuel (HVOF) [7] , flame spray [8] , screen printing [9] , and electrophoretic [10] techniques for use in applications such as corrosion protection. However, produc- tion of thick coatings with these methods is limited. Thick, dense metallic coatings can be produced using cold gas spray, but cold gas spraying of polymers is challenging due to their low densities and melting points along with lower stiffness. Impact Innovations developed a method to produce PEEK CONNECTING POLYMERS AND METALS USING COLD GAS SPRAY Coating development using cold gas spray technology demonstrates the feasibility of bonding polymers to metal substrates and metals to polymer composite substrates with good adhesion. Reeti Singh, Ján Kondás, and Christian Bauer Impact Innovations GmbH, Haun/Rattenkirchen, Germany 4 FEATURE coatings onmetallic substrates using cold gas spray. Metallic coatings on carbon fiber-reinforced polymer (CFRP) composites are of interest for lightning strike protec- tion of aircraft structural components. High-strength rein- forced composites are used in aircraft for weight reduction, but they cannot provide lightning protection due to their high electrical resistivity. Therefore, aircraftmanufacturers general- ly use lightning screens, which involve a complex, expensive manufacturing process. Recently, cold gas spray has been studied to determine the possibility of achieving lightning strike protection by coat- ing CFRP composites with electrically conductive materials, such as aluminum and copper. An Al coating was deposited directly on a carbon fiber-reinforced PEEK composite [11, 12] , but deposition of Cu required an Al bond coat [12] . A Cu pow- der-PEEK thermoplastic powder composite coating on the CFRP composite substrate has been used to increase bond strength between the coating and substrate [13] . It is difficult to deposit a pure metallic coating (e.g., Cu, Ag, Ti) by cold gas spray on CFRP composite substrates without a bond coat of Al. Current work demonstrates the feasibility of cold spray depo- sition of Cu and Ag on CFRP composite substrates without a bond coat. Fig. 1 — (a and b) Applying PEEK coating on steel substrate using Impact Innovation’s spray system (ISS) 5/8; (c) PEEK coating delamination after deposition; (d) PEEK coating with good bond strength. Fig. 2 — (a) Thick, dense PEEK coating (after machining) deposited on Al substrate; (b and c) cross sections of PEEK coating on Al substrate showing good interface quality.