Selective Stripping of Cadmium and Zinc-Nickel Coatings

Navy SBIR 24.2 - Topic N242-082
NAVAIR - Naval Air Systems Command
Pre-release 4/17/24   Opened to accept proposals 5/15/24   Closes 6/12/24 12:00pm ET    [ View Q&A ]

N242-082 TITLE: Selective Stripping of Cadmium and Zinc-Nickel Coatings

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.


  1. "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.
  2. "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.
  3. "Aerospace Material Specification: AMS QQ-P-416 Rev. G - Plating, Cadmium (Electrodeposited)." SAE International, Working Committee, September 2022.
  4. "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.

KEYWORDS: Cadmium; Cd; Zinc-Nickel; Zn-Ni; Stripping; Coatings; Corrosion; High-Strength Steel


The Navy Topic above is an "unofficial" copy from the Navy Topics in the DoD 24.2 SBIR BAA. Please see the official DoD Topic website at for any updates.

The DoD issued its Navy 24.2 SBIR Topics pre-release on April 17, 2024 which opens to receive proposals on May 15, 2024, and closes June 12, 2024 (12:00pm ET).

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Topic Q & A

6/03/24  Q. a) currently, how do you measure the thickness of the coating to be removed?
b) currently, what mechanism is being used by the supervisors/ technicians to ensure the coating removal does not extend far beyond the damage area?
c) do you have a grading system of the damaged areas ie Grade A, B, C or some sort of classification?
   A. a) Coatings are not measured for thickness prior to removal. It can be assumed that all cadmium or zinc-nickel coatings will be around 0.0005 inches and less than 0.0010 inches in thickness.
b) A visual inspection is done to determine the area that requires repairs. Anywhere that coatings are stripped, a touch-up application using brush plating would be required.
c) There is no grading system for cadmium/zinc-nickel corrosion damage; rather the assessment is primarily based on whether or not cadmium is still visually present on the surface where it should be. If not, then a cadmium repair and touch-up job usually will need to be performed.
5/23/24  Q. 1. How uniform and consistent are the zinc-nickel coatings and the cadmium coatings? Do these follow a mil spec standard or do the alloy compositions consist of a large variety?
2. Is an electrochemical solution acceptable for this solicitation?
3. At the I and O level operations are there restrictions on what type of mechanisms and sensors can be used to measure coatings as well as removing them?
4. What are the desired operating conditions for the stripping in terms of time, cost per process, level of protection of the underlying steel and occupational hazards?
5. What is the desired complexity for training an operator? I.e. should this be something an average NCO of average competency can be trained quickly to do or will this be something only specialists should be operating?
6. What type of environment will this likely be used in? Such as a specialized clean room or a hanger deck of a carrier..etc? Mainly for information on if we need to account for humidity, salty mist from sea water, dust from a desert…etc
   A. 1. Coatings are very uniform and consistent. Chemical composition of cadmium coatings is pure cadmium. Chemical composition of zinc-nickel coatings range between 12-15% nickel with remaining zinc. Thicknesses will be around 0.0005” +/- 0.0003” for both cadmium and zinc-nickel. Specifications include MIL-PRF-32660 and MIL-PRF-32648 for zinc-nickel, and AMS-QQ-P-416 for cadmium.
2. Yes.
3. If electricity is required, assume only 120V electricity is available. If water is required, assume only local tap water is available which can vary in quality around the world. Stripping may sometimes need to be done in tight spaces or on parts with complex geometries; assume that if a maintainer currently can reach their hand to touch the surface and as a direct line of sight to the surface, then the ideal solution should have a similar level of dexterity.
4. Stripping time should not exceed several hours; it is highly desirable to be able to do an entire repair procedure (strip, inspect, repair, re-coat) within a standard 8-hour working shift. Cost is not part of the evaluation at this stage, but of course lower operating costs are better. The stripping method used should not damage underlying steel. The focus of this project is to reduce occupational exposure to cadmium or zinc-nickel for the maintenance personnel; an ideal method should not introduce new or additional occupational hazards that need to be mitigated with other safety methods.
5. This would be used by average maintenance personnel and not by specialists. Training should be able to be accomplished quickly and with minimal complexity.
6. This will most commonly be used in aircraft hangars or other maintenance shop space. Temperature and humidity can vary based on the operating location, but there would be no salt mists or dust blowing in the work area while the work is being performed.
4/30/24  Q. Q: Will the selective stripping of cadmium/zinc-nickel be done on any munitions/missiles/warheads?
Q: Once the cadmium/zinc-nickel is stripped, how is the coating re-applied onto the part?
   A. A: No. The stripping process will occur only on aircraft components.
A: The coating is re-applied through a brush electroplating process.
4/26/24  Q. Are you seeking solutions that don't use abrasives in any capacity? In other words, if maintainers weren't involved in the process but wet sanding was still performed, is that an acceptable option?
   A. We will consider abrasive methods of removal also. If using an abrasive method, please ensure there is a method to capture and contain all dust and HAZMAT, to eliminate exposure risks to maintainers and others in the work area. Please also keep in mind that whatever method is developed must have a high level of dexterity to reach into tight areas. Assume that if a maintainer can see and reach their hand into an area, then your method should also be able to reach the surface where the coating is.
04/22/24  Q. TPOC provides Frequently Asked Questions for DoN SBIR Topic N242-082 - Selective Stripping of Cadmium and Zinc-Nickel Coatings

Q1: What is meant by depot, intermediate, and organizational level maintenance?
Q2: Does this method need to remove both cadmium and zinc-nickel?
Q3: What is the typical thickness of coating to be removed?
Q4: How will testing for this stripping method be performed?
Q5: Are parts removed from aircraft when this maintenance procedure is done?
Q6: What shapes/geometries will the components have? How accessible are the areas being repaired?
Q7: Will the aircraft component have primer/topcoat/other coatings on it?
Q8: How strict is the 1-2 hour time limit that is specified?
Q9: Portability requirements?
Q10: Is hazardous waste generation allowed?
   A. A1: Here are two links that may give you a better understanding of the levels of maintenance. This project focuses on developing a cadmium and zinc-nickel stripping method primarily to be used at the organizational and intermediate levels (also known as field levels), where they do not have the specialized infrastructure that depot level facilities have.
A2: Methods that remove both types of coatings will be strongly preferred. There are many aviation components that use both cadmium and zinc-nickel coatings. For ease of maintenance, this stripping method should be able to address both coatings.
A3: Typical coatings to be stripped will range from 0.0002 - 0.0010 inches in thickness.
A4: Corrosion testing will be done in accordance with ASTM B117. Hydrogen embrittlement testing will be done in accordance with ASTM F519.
A5: Sometimes they are, but many times they are not. Assume that the stripping method being developed must work while parts are on the aircraft.
A6: Shapes of the components can range from fairly simple and easily accessible flat or cylindrical surfaces (such as landing gear), or much more complex geometries on parts internal to an aircraft. The components that need repair currently have cadmium removed using a wet sanding method, where maintainers abrade the surface using sandpaper. For maintenance accessibility, your method of stripping should allow for a similar amount of dexterity.
A7: Before the cadmium/zinc-nickel stripping step, any other coatings on the part will be removed using other methods. For this project, only stripping cadmium or zinc-nickel is necessary.
A8: That timeframe is given as an estimate, and of course methods that work more quickly are preferred. The intent of this requirement is to approximately match how long a cadmium or zinc-nickel stripping job currently takes, and to ensure that a full repair job (i.e. prep work, stripping old coatings, and then applying new touch-up coatings) will fit into one 8-hour work shift.
A9: Because this maintenance procedure is meant to be performed at field level sites, the overall portability and ease-of-use of the stripping system is important. Maintainers should be able to easily move or carry the system to and from various aircraft maintenance jobs. The system should not require large or unusual infrastructure; for example, you may assume that all maintenance sites have basic services like 120-volt electricity and potable water.
A10: Yes, aircraft maintenance procedures sometimes generates hazardous waste. Maintenance sites do have methods for hazardous waste disposal. However, hazardous waste generation should be minimized as much as possible.

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