THREADED FASTENER COATINGS FOR AEROSPACE APPLICATIONS(C)

Threaded fasteners used in jet engines experience seizing/galling prob lems due to exposure to high temperatures, corrosive environments, and vibration. Silver coating is commonly used to prevent sating and gall ing. However, silver attacks waspaloy when exposed to high temperature s and spreads outside the fastener and reacts with various materials u sed in the engine. Alternative high-temperature coatings are selected based on their thermal, oxidative and tribological properties. Physica l vapor deposition (PVD) and sol-gel techniques were used to deposite these coatings on waspaloy coupons and fasteners. The coatings were ch aracterized by Auger electron spectroscopy and optical microscopy befo re and after thermal treatments. Selected coatings were applied on fas teners which were then assembled and exposed at 650 degrees C in air f or 100 hours. The torques were measured during assembly and disassembl y. Titanium nitride and palladium-coated fasteners showed the most con sistent and low values of the ratio of break-loose torque to assembly torque.