Impact wear resistance of nanocomposite coatings for aircraft components

Landing gear is an aircraft component often subjected to wear, fracture, mechanical failure and erosion, principally caused by impact with sand and other small particles. Erosion wear can cause deformation and material removal with consequent efficiency reduction. Coatings can protect stressed structural part and impede the erosion of the metallic components. This work focus on the investigation of the erosion resistance of two ceramic multilayer coatings, AlSiTiN and AlSiCrN, deposited by Physical Vapour Deposition (PVD) on a high speed steel (H11) usually used for landing gear application. Erosion test were carried out with an erosion machine using alumina particles. Powder was directed to the specimens (coatings and substrate) at nominal impingement angles of 90° and 20° with different impact speed (50, 75, 100 and 125 m/s at 90° and 100, 125, 150 and 175 m/s at 20°), at a nozzle-specimen distance of 10 mm. All the tests were performed for two minutes. Hardness and Young's modulus were obtained by nanoindentation, and adhesion between coating and substrate was evaluated by scratch test. Volume lost was measured with Taylor Hobson profiler while cracking behaviour and microstructure modifications were examined with a scanning electron microscope (SEM). AlSiCrN coating significantly enhanced the erosion resistance of H11 substrate, showing higher resistance also with respect to AlSiTiN coating. Indeed, the coating was not completely removed from the surface neither at 90° nor at 20°. The erosion wear rapidly increased by increasing the impact speed in the case of substrate and AlSiTiN, while such parameter was not significantly influent in the case of AlSiCrN. The results suggest that adhesion should play an important role to explain the highest erosion resistance of AlSiCrN coating. Erosion mechanism was principally driven by the intrinsic brittleness of both ceramic coatings.