The Application of Thermal Spray Coating Technology for Lightning Strike Protection of Zone 1A 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 smaller aircraft such as Evektor’s EV-55. One of the biggest problems in building and certifying an all-composite airframe is lightning protection. Traditionally, lightning strike protection (LSP) has been provided by embedding expanded metal foil (EMF) just below the surface of fibre reinforced composites. However, this is a costly, highly specialised manual process. TWI has developed thermally spray coatings as an alternative LSP system. Metallic coatings are applied to CFRP post-manufacture and offer significant benefits in terms of performance, ease of manufacture, damage tolerance and repair. Metallic coatings can be deposited on a wide range of substrates, including epoxy based CFRP, BMIs and other high temperature resin systems, eg polyimide and phenolic resins. However, care must be taken over selection of material, spray process and parameters. The technology has significant benefits as it can be applied to double curvatures and complex geometries and is only restricted to the line of sight and spray distance requirements of the thermal spray process. Coatings can be applied as either continuous layers or discrete areas of coatings 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 investigates the application of metal sprayed coatings for Zone 1A lightning strike protection. The relationship between the sheet resistance and grams per square metres of aluminium and copper thermal spray coatings is evaluated, along with the lightning strike performance in Zone 1A regions. Upscaling of the technology for commercial applications is also considered, alongside the galvanic compatibility of the metal sprayed coatings with CFRP substrates for commercial applications.