Sol–gel derived erosion protection coatings against damage caused by liquid impact

Abstract

Erosion protection coatings are developed and characterised in order to protect aeronautic structures susceptible for damage caused by liquid and solid impact, e.g. the leading edges of the wings, the radome or the leading edges of rotor blades. Substrates for all coatings are aluminium alloys (AA2024) coated by an epoxy primer. There are two principle sources for erosion damage: sand and rain erosion. This study focuses on the development and characterisation of transparent sol–gel coatings resistant to rain erosion. The impact of the hardness of the coatings on the erosion protection performance is investigated by varying the ratio of organic-rich to inorganic-rich compounds. Additionally, the mechanical properties of the resulting hybrid coatings are adjusted by nanoparticles (e.g. ZrO 2). Samples are coated by dip-coating. All developed coatings are analysed regarding their adhesion (cross cut), flexibility (impact, mandrel-bending), hardness (nanoindentor) and rain erosion resistance (Stationary Sample Erosion Test). The effect of nanoparticles in sol–gel coatings on the erosion protection behaviour is investigated by scanning electron microscope. All sol–gel coatings showed excellent flexibility and adhesion to the substrate. The deformation behaviour of the coatings is visco-elastic. The evaluation of the results obtained from liquid impact tests shows cohesive failure of the coatings without any sign for delamination. Compared to commercialised erosion protection coatings, particle reinforced hybrid sol–gel coatings increase the resistance against rain erosion. Furthermore, the weight of the protection system is decreased due to the fact that sol–gel coatings reduce the required layer thickness.