Cold spray is a reduced temperature, supersonic thermal spray process that is increasingly being used to perform repairs on high value components. In this case, a valve actuator internal bore sealing surface was repaired on an aluminum 6061 hydraulic valve body using high pressure cold spray. Corrosion damage to non-critical surfaces was also repaired, allowing the part to be returned to service. The VRC Gen III high-pressure cold spray system was used to deposit gas atomized 6061 aluminum powder. The internal bore surfaces were approximately 100 mm in diameter with a depth of nearly 200 mm, and were sprayed using a 45-degree nozzle 65 mm in length. The minimum required adhesion strength on critical surfaces was 69 MPa. The average adhesion strength was 71.4 MPa, with glue failures on ASTM C633 bond test specimens.

Problems with corrosion resistance in hydraulic cylinders used in marine environments contribute to many failures. Thermal spraying has proven to be a reliable method for replacing electroplated coatings in aircraft, but performance in high corrosive environments is still a drawback. In the present work, a new sealing method to densify WC-CoCr HVOF coatings is tested, which appears to be applicable to hydraulic cylinders in marine environments. The method is based on the use of nanoparticle solutions that penetrate and fill pores and cracks to seal the coatings. Two such solutions are tested and compared to as-sprayed coatings. Open-circuit potential and tribocorrosion measurements in 3.4% NaCl show that sealed coatings are more resistant to corrosion and wear than as-sprayed layers.

Environmental constraints on exposure to hexavalent chrome and its compounds has prompted increased utilization of HVOF thermal spray coating technology to implement new overhaul repairs for components that are currently chrome plated. Proposed 1998 EPA and OSHA standards place very tight restrictions on the Personal Exposure Limit (PEL) for hexavalent chrome, which will impact chrome plating operations and most likely attendant grinding operations. Historically, HVOF or D-gun type repairs involved bearing bores, journals on main shafts, mid span supports, dimensional restorations and clearance control applications predominantly on gas turbine engines. Currently, the Naval Aviation Depot Jacksonville is further developing HVOF capabilities for repairing all P-3 aircraft hydraulic component piston rods, landing gear piston struts, and landing gear axle journals with a tungsten carbide 17% cobalt coating in lieu of chrome plating. Once implemented, the repair technology will be transferred to other Naval aircraft components beginning with F14, F/A-18, EA-6B, E-6, and will eventually reduce personnel exposure to chrome and reduce environmental disposal costs for chrome plating waste by two-thirds. This paper provides a case study of the development and implementation of a chrome plating replacement for the P-3 aircraft including fatigue, corrosion, and seal wear testing, as well as HVOF parameter optimization development.

Due to advanced technical, economic and environmental reasons, radial shaft and hydraulic rod seals demand new wear resistant counterface materials. Thermal spraying offers one alternative to common hardening and hard plating technologies. Applying corrosion resistant ceramic coatings by Thermal Spraying leads to new applications in sealing systems. The combination with PTFE-compound sealing materials can be used with aqueous, non-lubricating and corrosive fluids. The authors have carried out extensive research on how the coating material and the surface structure of the coating effect hydraulic rod and radial shaft sealing systems. The presented results show that the influence of the coating on the sealing is critical for the performance of both standard and new custom sealing systems.