Thermal spray coatings for lightning strike protection of composite aircraft structures

Carbon fibre reinforced polymer (CFRP) features in the latest generation of aircraft such as the Boeing 787, Airbus A350 and Bombardier C-Series, and as such lightning protection is a critical factor in the safety of these aircraft. Traditionally, lightning strike protection on composite aircraft components has been provided by embedding expanded metal foil just below the surface of fibre reinforced composites during manufacture. However, this is a costly, highly specialised manual process. Alternative approaches involve modification of the composite materials eg by mixing resins with metal flake or fibres or by developing intrinsically conductive polymer (ICP) blends for this purpose. TWI has developed thermally spray coatings as an alternative lightning strike protection system. Metallic coatings are applied to CFRP post-manufacture and offer significant benefits in terms of performance, ease of manufacture and also damage tolerance and repair. The metallic coatings can be deposited on a wide range of substrates including epoxy based, BMI and other high temperature resin systems such as polyimide and phenolic resins composite parts. Care must be taken with selection of material, spray process and parameters. The technology can be applied to double curvatures and complex geometries and is only restricted to the line of sight and spray distance requirements for the particular thermal spray process. The coatings can be applied as either continuous layers or on discrete areas tailored to the lightning zoning requirements. TWI has demonstrated the feasibility of applying these coatings over large scale components, of the order of metres, and that repair of the coatings is possible. This paper covers the application of thermal spray coatings for lightning strike protection and other applications such as electromagnetic interference (EMI) and radio frequency interference (RFI) shielding applications and data transfer technology and upscaling the technology for commercial applications.