Electrodeposition of Nanocrystalline Co-P Coatings as a Hard Chrome Alternative



This project will demonstrate/validate and qualify pulse-electroplating technology for deposition of nanocrystalline cobalt-phosphorus (nCo-P) coatings as a replacement for electrolytic hard chrome (EHC) plating for weapon systems. nCo-P coatings were successfully developed under SERDP project WP-1152 and scaled up in ESTCP project WP-200411. These projects showed that the nCo-P coatings have properties that are equivalent to and in many ways better than EHC.

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Technology Description

The nCo-P coatings are produced by electrodeposition from a fairly standard aqueous solution using cobalt rounds as anodes. Like the EHC electrodeposition coating process, nCo-P deposition is an aqueous bath process. The deposit is very similar in appearance to EHC; however, nCo-P has a nanocrystalline grain structure with an average gain size of 5-15 nm. The reduced grain size results in improved material properties, including enhanced corrosion protection, sliding wear performance, hardness, and tensile strength. Since nCo-P deposition is an aqueous method, it can be used in any application currently served by EHC and likely also any application in which thin dense chrome (TDC) is presently used. It has even been brush plated, making it a viable option for localized intermediate-level repair, which is very important for battle readiness in systems deployed overseas. High-velocity oxygen fuel (HVOF) thermal spray is being broadly implemented by the depots in place of EHC on line-of-sight surfaces due to its improved performance, especially in situations where EHC experiences high wear. This project addresses the following remaining needs for hard chrome replacement: (1) a depot maintenance EHC alternative for non-line-of-sight surfaces, and (2) a single process for simultaneous plating of both internal and external surfaces of complex components. It does not address TDC, which is not used in depots, or brush plating.

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Interim Results

The nCo-P plating process was developed under SERDP project WP-1152. The data showed that the performance of the material is essentially equivalent to EHC in sliding wear and better in corrosion and hydrogen embrittlement, although embrittlement performance appeared to change under modified deposition conditions. Abrasive wear performance of tested coatings was somewhat lower than EHC, but performance of the fully optimized material will depend on its hardness and hence on the P content, which can be increased, although that reduces the strain tolerance of the coatings. Scale-up and further demonstration of the nCo-P technology was conducted under ESTCP project WP-200411. As part of this project, the nCo-P system was successfully scaled up at Integran to a 300-gallon demonstration system. This system has been in operation for 44 months, with no major deviations in deposit quality to date. Operating parameters and process sensitivity have been defined. This system was used to plate coupons for performance testing in accordance with a Joint Test Protocol. In addition to scale-up at Integran, the nCo-P technology was transferred to the Navy's Fleet Readiness Center - Southeast (FRC-SE) in Jacksonville, Florida. A 250-gallon demonstration system was installed and selected aircraft components have been successfully coated.

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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. Implementation of the technology will eliminate environmental and worker safety concerns associated with the hexavalent chromium used in the EHC process. 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. (Anticipated Project Completion - 2013)

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Points of Contact

Principal Investigator

Mr. Ruben Prado

Fleet Readiness Center

Phone: 904-790-6381

Fax: 904-790-6379