Cold Spray Coatings for Chromium and Nickle Plating Replacement

Mr. Victor Champagne | U.S. Army Research Laboratory



Research focused on the synthesis of cold spray (CS) powders, innovative nozzle design, and optimized CS process parameters is needed to develop environmentally benign processes to replace electrolytic chromium (Cr) and nickel (Ni) plating used in localized areas on steel and aluminum alloys. CS will enable the Department of Defense (DoD) to comply with environmental regulations (i.e., AERTA PP-2-02-04) and Executive Orders (EOs) to eliminate chromic acid, a hazardous substance containing hexavalent chrome, a known carcinogen, and Ni, also known to be an environmental and occupational pollutant, while adhering to the DoD Strategic Sustainability Performance Plan. EO 13148 requires the reduction of hexavalent chromium by 50%. Moreover, the Occupational Safety and Health Administration (OSHA) has proposed a reduction in the current Permissible Exposure Limit (PEL) established for water soluble chromium (VI) compounds from the current 5 micrograms per cubic meter (µg/m3) to less than 1 µg/m3. The objective of this project is to develop powdered materials that can replace electroplated Cr and Ni as well as the CS parameters needed for their acceptable application.

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Technical Approach

This project will use a “Materials by Design” approach to develop an understanding of the fundamental principles associated with feedstock powder characteristics and their relationship to nozzle design, as well as optimal CS process parameters and the resultant CS coating. Thermodynamic, kinetic, and solidification models will be used as a foundation to determine the effects of composition, solidification conditions, and heat treating techniques on the microstructure and resulting mechanical properties of the powder particles. Flow modeling through computational fluid dynamics (CFD) and analytical approaches will be used to predict particle velocity, temperature, and distribution within the CS gas stream. A particle impact model developed by the Army Research Laboratory and applied to well-known computational solvers for flow stress and hardness that has been proven to predict the hardness of CS coatings will be incorporated to determine the particle impact characteristics and to predict bonding and adequate particle consolidation. This will allow for the development of specific CS powders that will have the necessary characteristics to meet the requirements of current Cr and Ni electroplating coatings. Subsequent to the development of CS feedstock powders and optimized CS process parameters, spray trials of the newly developed CS powders and extensive materials characterization will be conducted in order to better understand the particle/substrate interactions and bonding mechanism of CS coatings to meet or exceed the requirements for Cr and Ni electroplating with respect to adhesion, hardness, density, and corrosion and wear resistance.

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This work will advance the state-of-the-art for CS by providing a better understanding of the particle/substrate interaction and bonding mechanism, and result in novel CS coating materials that can be used by DoD and industry to replace Cr and Ni electroplating. It will eliminate hazardous materials associated with Cr and Ni electroplating while providing a superior coating utilizing a process that is also mobile for field repair. CS applications are vast and include shafts, splines, gears, landing gear, seals, housings, and gun barrels. The total cost savings of this approach is estimated to be at least $5 million per year based on data provided from the National Defense Center for Energy and Environment (NDCEE) Toxic Metal Waste Study, and yearly production numbers and associated waste disposal costs collected from Watervleit and Rock Island Arsenals and the Corpus Christi and Anniston Army Depot. (Anticipated Project Completion - 2018)

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Points of Contact

Principal Investigator

Mr. Victor Champagne

U.S. Army Research Laboratory (USARL)

Phone: 410-306-2719