Silver-based conductive coatings as lightning strike protection for composite aircraft

Lightning strike protection of composite structures is an increasingly studied subject in the aerospace industry due to the need for finding novel protection solutions for low conductive composites. This work presents two silver-based lightning protective conductive coatings for potential replacement of expanded copper foil (ECF) as lightning strike protection (LSP). The first solution consists of an electroless method to produce silver-coated carbon fibres (SCCF). The SCCF are integrated as a sacrificial ply on a carbon fibre reinforced polymer (CFRP) panel with four different areal densities, using an epoxy-based primer or a PEDOT:PSS conductive ink as binder. The second solution is a silver-based commercial product consisting of a two-part epoxy with silver flakes, which acts as a sprayable thin coating beneath the paint layer. The protected CFRP panels were covered with aerospace-grade paint for realistic finishing and were subjected to high impulse current strikes. All four conductive coatings containing SCCF exhibited around 45%–50% retention of flexural strength, although largely inferior to painted expanded copper foil's resistance to emulated lightning strikes. The silver-based commercial product showed 83% retention of flexural strength and 97% retention of effective bending modulus, with a comparable performance to the painted expanded copper foil. The resulting retention of flexural strength, the absence of severe damage to the structure, its versatility for complex geometries and the easy manufacturability of the silver-based commercial coating makes this approach a good candidate for the replacement of ECF as a solution for LSP.