Cadmium (Cd) and hexavalent chromium (Cr6+) have long been widely used in DOD weapons systems, along with many aircraft, automobiles, trucks, and other large commercial vehicles because of their corrosion and wear-inhibiting properties. Yet both cadmium and hexavalent chromium (hex chrome) are known carcinogens. To protect maintainers and the environment, the CTMA Program launched a collaboration to replace parts plated with Cd and CR6+ for Army ground vehicles. The replacement chosen is Zinc-Nickel (Zn-Ni) coatings. The initiative combined the expertise of multiple Army logistics teams and industry partners BAE Systems, Booz Allen Hamilton (BAH), and MNP Fasteners.
This project is extremely labor-intensive, as the collaborators must examine all engineering drawings containing thousands of parts, identify which of those parts contain Cd and Cr6+, determine how many times each identified part is used, prepare needed source data for engineering change proposals to update drawings containing Cd/Cr6+ parts, and document the transition process to ensure repeatability for other platforms. To speed up this process, the team has been using an AI tool that automatically identifies the individual part numbers that need to be abated and assigns the replacement part numbers on the drawing.
“We are now moving forward on removing these hazardous materials from the Ground Vehicle systems, which the Army has been intent on doing for quite some time,” says Matthew Withun, an engineering and management consultant at BAH and the project manager who is overseeing the abatement execution for PEO Ground Combat Systems.
Laboratory and field test results have indicated that Zn-Ni coatings (approximately 85 percent zinc and 15 percent nickel, electroplated on carbon steel) are as or more effective than cadmium and hex chrome coatings, and they do not contain any known carcinogens. Zn-Ni coatings offer superior corrosion protection, excellent wear resistance for mechanical parts, and superior performance in high-temperature environments. These benefits have led automotive manufacturers to make the wholesale change to Zn-Ni coatings. Moreover, initial estimates show that the cost of Zn-Ni is comparable to that of cadmium and hex chrome-plated parts, for larger orders (5,000 or more pieces).
The CTMA collaboration’s goal is to facilitate DOD-wide adoption of Zn-Ni to replace hazardous cadmium and hexavalent chrome, providing a safer work environment for maintainers, soldiers, and depot personnel. In the project’s first phase, the team began a pilot to identify and replace cadmium and hex chrome-plated parts in one weapons system: the M109A7 (Paladin), which is currently fielded by the US Army. The team analyzed the M109A7 and identified over 3,000 unique fasteners (bearings, bolts, brackets, clamps, connectors, nuts, pins, screws, springs, and washers), about 900 of which contained cadmium/hex chrome coatings and were flagged for abatement. Moreover, the team authored and published the MIL-PRF-32647 Performance Specification for Zinc-Nickel Electroplating for Fasteners. As a result, the American Society of Mechanical Engineers (ASME) Standard B18-24 was revised to include this Zn-Ni finish option.
The project, now in its second phase, is demonstrating the transition of the M109A7 and M992A3 vehicles to Zn-Ni hardware (fasteners, connectors, and mechanical components) and documenting the transition process to ensure repeatability for other platforms.
“I’ve been helping to manage the impacted assemblies and installations where all this hardware resides,” says Linda Knisley, Senior Principal Environmental Engineer, CSEP Combat Vehicles, BAE Systems Platforms & Services. “We created a validation plan, including over 1,400 fasteners, and tested their capabilities out in Yuma (YPG). The Zn-Ni fasteners performed at least as well as the legacy fasteners, if not better in many cases.”
An AI tool developed by BAH has greatly facilitated this process. “BAE pulled PDFs of all the drawings and created a cross-reference file of all the fasteners that needed to be abated and their corresponding compliant part numbers,” says Knisley. “We fed those into the AI tool, which cuts down a lot on time and it will improve the accuracy because these are 18-digit part numbers that could be transcribed inaccurately if done manually.”
As of March 2022, the team has reviewed 99.8% of the identified fastener part numbers in the M109A7 and, so far, have determined solutions for 98% of those requiring abatement. For the M992A3, the team has reviewed 96% of the identified fasteners and have solutions for 95% of those requiring abatement. In addition, the team is working on establishing effective contracts with companies that manufacture Zn-Ni plated fasteners to ensure a constant, cost-competitive supply of parts with multiple supplier options.
Because the collaborators are carefully documenting their work process, other Army program teams, services, and commercial organizations will be able to easily model their programs to transition their specific platforms to Zn-Ni alloy coatings. The Army is now prioritizing the next legacy systems for complete replacement of parts plated with cadmium or hexavalent chromium with Zinc, which could include the Bradley, AMPV, M88 Recovery Vehicle, Extended Range Cannon Artillery (ERCA), and Field Artillery Ammunition Supply Vehicle (FAASV).
“This capability has generated a lot of interest,” says Withun. “The Air Force has contracted to have the BAH AI tool provide similar services. The AI tool can be used to scrape data from various government sources, merge those datasets together, and provide insights from the combined dataset that would be difficult to obtain otherwise.”