The objectives of this project are to demonstrate and validate (1) pulsed electrodeposition of nanocrystalline cobalt-phosphorus (nCo-P) coatings, either in bath or brush plating, as a viable alternative to electrolytic hard chrome (EHC) plating on internal surfaces and complex geometries; and (2) nCo-P coatings as a viable replacement for thin dense chrome (TDC) on selected components for new military aircraft.
Nanocrystalline cobalt-phosphorus coatings were developed under the SERDP project WP-1152. This technology uses pulse plating to control the nucleation and growth of grains within the coating, creating a nanocrystalline structure. Testing indicated that coating application does not cause hydrogen embrittlement of high-strength steels, which is a significant problem with EHC plating. Performance testing showed that the nCo-P coatings demonstrated superior salt-fog corrosion and pin-on-disk wear behavior compared to EHC coatings, with abrasive wear performance slightly less than for EHC coatings. The nCo-P coatings can be deposited to thicknesses ranging from 0.0001 to 0.020 inches, making them potential alternatives to both EHC and TDC. This technology is a direct drop-in for the existing EHC process and may be incorporated into existing plating lines, although this would require replacement of plating power supplies.
In this project, a 100-gallon nCo-P demonstration plating tank will be installed at Naval Ammunitions Depot (NADEP) Jacksonville and a brush plating system will be installed at Ogden Air Logistics Center (ALC). A demonstration plan, incorporating a joint test protocol (JTP), will be developed by stakeholders. The JTP will include both materials and component tests, utilizing EHC as a baseline. The environmental and cost impact of inserting this technology into repair depots will be evaluated, including implementation, processing and life-cycle costs, and waste reduction. The nCo-P coatings also will be assessed as a replacement for TDC on the ring gear of the Joint Strike Fighter leading edge flap actuator. Other potential TDC replacement applications will be determined.
Successful demonstration and validation of the nCo-P plating technology should lead to its implementation at several military repair depots, since it functions as a direct drop-in replacement to EHC. This will eliminate environmental and worker safety concerns associated with the hexavalent chromium found in EHC. Since the coating does not contain nickel, environmental concerns related to the nickel content of EHC alternative coatings also will not be an issue. The superior corrosion and sliding wear performance should lead to reduced life-cycle costs, and the elimination of hydrogen embrittlement concerns will result in significantly reduced turnaround times for component repairs.