OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials; Sustainment OBJECTIVE: Develop a method for selectively stripping cadmium (Cd) and zinc-nickel (Zn-Ni) coatings from small areas (i.e., several square inches/centimeters) on high-strength steel components, without generating dusts that pose an inhalation risk. DESCRIPTION: Cadmium (Cd) coatings and Zn-Ni coatings are used on many high-strength steel components on aircraft, such as landing gear assemblies on fixed-wing aircraft and the rotor masts of rotary aircraft. These coatings prevent corrosion and protect the integrity of the underlying steel. However, over time as the coating gets damaged or worn, the coating must be removed and repaired. For parts that are overhauled at the depot level (D-level), spent Cd or Zn-Ni coatings can be stripped by immersing the part in a chemical tank. After the coatings are stripped, the underlying metal can be inspected, repaired as necessary, and then recoated with fresh Cd or Zn-Ni coatings. Depot level facilities have chemical processing plants that allow for this type of work to be performed safely. However, this chemical process is not feasible to perform at intermediate (I-level) or organizational (O-level) level maintenance facilities. Dozens of I-level and O-level facilities around the world perform touch-up repairs of Cd or Zn-Ni coatings on aircraft components, often to fix localized damage that requires stripping and recoating several square inches (centimeters) of surface area. To remove the old coating when a chemical processing plant is not available, maintainers use methods such as hand sanding, wet sanding, or abrasive blasting to abrade away the Cd or Zn-Ni layer. Unlike with full immersion in a chemical processing tank, using abrasive methods to remove coatings generate inhalation and exposure risks to the maintainer, as well as to the surrounding environment. Particularly with Cd coatings, Cd is carcinogenic and long-term exposure can increase the risk of various cancers and other health effects. There have also been cases where maintainers use an incorrect abrasive that is too aggressive, inadvertently causing damage to the component they are processing. This results in increased rework costs and delays in returning the component to the fleet. This SBIR topic seeks a method for stripping Cd and Zn-Ni coatings that generate no inhalation exposure risks for maintainers, eliminates the possibility of Cd dust release into the maintenance hangar or surrounding environment, and a method that is repeatable and easy for maintainers to use with no risk of causing inadvertent damage. An ideal solution should be able to remove both Cd and Zn-Ni coatings, be simple and cost-effective, and be easy to deploy to I-level and O-level maintenance sites around the world. The method must selectively strip Cd and Zn-Ni coatings without damaging other coating types, such as primers and topcoats. The method must also not damage the underlying steel component, such as through corrosion or hydrogen embrittlement. PHASE I: Develop a concept for a Cd and Zn-Ni removal system that can selectively remove these coatings from selected areas of aircraft components, while reducing worker and environmental exposure to toxic or carcinogenic materials. Demonstrate the feasibility of the stripping method, evaluating parameters such as stripping effectiveness, stripping duration, hydrogen embrittlement risks, and the overall ease of use. Prepare a report on the designed method, as well as a Phase II test plan. The Phase I effort will include prototype plans to be developed under Phase II. PHASE II: Prepare a prototype system for Cd and Zn-Ni removal that reduces exposure to toxic or carcinogenic materials. Assess and optimize key parameters such as system portability, material compatibility, impact to the underlying substrate, process costs, and maintainer ease-of-use. Evaluate and ensure that there are no adverse effects to the substrate through the use of this method, such as inadvertent pitting, etching, corrosion, or hydrogen embrittlement. Provide a report that documents the design of the prototype system, results of system performance, and the results of the material testing. Provide a prototype stripping system to NAVAIR for evaluation. PHASE III DUAL USE APPLICATIONS: Ensure that product functions as intended, stripping Cd and Zn-Ni coatings within a reasonable amount of time (~1 2 hr), and does not produce any detrimental effects to the base substrate. Have the product made into a commercial product that is available for widespread distribution. Create a National Stock Number (NSN) for the product so that it can be easily procured by Department of Defense (DoD) maintenance activities worldwide. This product has applications both in military and in commercial aviation maintenance activities. Cd and Zn-Ni has widespread usage as coatings for corrosion protection on high-strength steels, including on commercial airliners, passenger helicopters, corporate jets, and general aviation aircraft. Removal of these coatings is a common maintenance task on all types of aircraft, and a method of removing these coatings without producing hazardous dusts is highly desirable. REFERENCES: MIL-STD-871 Rev. D Department of Defense standard practice: Electro-chemical stripping of inorganic finishes. Department of Defense, U.S. Air Force, 20 June 2019. http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-871d_56035/ MIL-STD-865 Rev. E Department of Defense Standard Practice: Selective, Brush Plating, Electro-Deposition. Department of Defense, U.S. Air Force, 9 May 2019. http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-865E_56027/ Aerospace Material Specification: AMS QQ-P-416 Rev. G - Plating, Cadmium (Electrodeposited). SAE International, Working Committee, September 2022. https://www.sae.org/standards/content/amsqqp416g/ MIL-PRF-32660 Performance Specification: Plating, Zinc-Nickel Alloy, Low Hydrogen Embrittlement, Alkaline Electrodeposited. Department of Defense, Naval Air Warfare Center Aircraft Division, Lakehurst, 10 November 2020. http://everyspec.com/MIL-PRF/MIL-PRF-030000-79999/MIL-PRF-32660_57042/ KEYWORDS: Cadmium; Cd; Zinc-Nickel; Zn-Ni; Stripping; Coatings; Corrosion; High-Strength Steel
