For a long time, the U.S. Department of Defense (DoD) (Arlington, Virginia, USA) says it decommissioned numerous high-value military vehicles due to corrosion damage. Without adequate repair technologies available, maintenance members faced enormous costs and downtime whenever they tried to fix and replace corroded vehicle parts and armor pieces.
In 2016, corrosion damage to military ground vehicles alone cost the U.S. Army about $1.2 billion.
But now, researchers at the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory (ARL) (Aberdeen Proving Ground, Maryland, USA) say they have refined their high-pressure cold spray repair technique to the point where it has now become the military’s preferred solution to corrosion damage and dimensional restoration.
“This is a repair technology that has been a godsend to the Department of Defense,” says Victor Champagne, an Army senior materials scientist. “Our work in cold spray has saved the military millions of dollars, not just for the Army, but [also] for the Navy, the Air Force, the Marines, and the Coast Guard.”
Cold Spray Process
During the cold spray process, researchers use high-pressure gases to accelerate metal particles at supersonic velocities onto the target surface. Upon impact, the particle deforms and flattens out as it binds to the substrate. A high-pressure cold spray machine can deposit layers upon layers of material onto vehicle parts to fill in cavities and coat surfaces.
Since cold spray doesn’t require heat to bind the materials, maintenance units can perform repairs on thermally sensitive components that would normally melt or otherwise be compromised with a traditional approach like thermal spray or welding. The technology also grants the user a tremendous amount of control and precision over the location of the coating and its properties.
“The Army Research Laboratory immediately recognized the value of this new repair technique,” says Aaron Nardi, team lead of the laboratory’s Cold Spray Center.1 “It took quite a while to develop the technology to the point where it could be inserted and used. A lot of concepts in those early days are really just coming to fruition now.”
Advancement of the Technology
The lab’s connection to cold spray stems back to the early 2000s, when researchers first introduced the technology to Army leadership. In 2001, Champagne established the lab’s Cold Spray Center after he developed the technology to the point where it could be transitioned. He worked with Anatolii Papyrin, an early Soviet Union pioneer of cold spray technology in collaboration with Sandia National Laboratories.
Champagne and his colleague Dennis Helfritch, along with the South Dakota School of Mines (SDSM) (Rapid City, South Dakota, USA), designed their own cold spray system based on the needs of the DoD and industrial base. From there, they greatly improved upon its capabilities.
This system was commercialized through a joint ownership agreement between the laboratory and SDSM, and a company called VRC Metal Systems (Box Elder, South Dakota, USA) emerged as the commercial producer of the system in 2012. According to the Army, the VRC system far exceeded the performance of its predecessors.
From there, a combination of advanced material science research, hardware improvements, and applications development helped to transform the ARL Cold Spray Center into a premier facility at the forefront of cold spray innovations.
In particular, the Army says the center’s success comes primarily from its goal to look at cold spray from a holistic perspective, taking into account every aspect beginning with feedstock powders. Another factor is the researchers’ determination to transition the technology across the DoD. As part of that process, the laboratory created feedstock powders specifically tailored for the cold spray process.
The center’s approach continues to this day by Nardi, who perfected the process alongside Army researchers during his time at the United Technologies Research Center (East Hartford, Connecticut, USA) before he was hired by the laboratory. Specifically, they engineered high-strength and high-ductile powders so that the material deposited by the gas nozzle not only bonded strongly with the substrate, but also possessed strong properties, which allowed superior coatings and materials to be developed.
“Cold spray deposits back then were very hard but brittle, like glass,” Champagne says. “We improved the powders to the point where we could cold spray materials that were impossible to do before.”
Over the past 20 years, Army researchers identified thermal treatments, particle size optimization, and multiphase powder formulations. These achieved high bond strength, toughness, and even ductility in materials ranging from aluminum and steels to cobalt and nickel-based compositions.
A lot of work also went into standardizing the cold spray process to keep the performance and the results consistent. Army researchers developed all aspects of powder synthesis and production down to the atomic level, as well as the proper packaging, shipping, and storage methodology to ensure the best conditions from start to finish for commercial production.
Extensive Cost Savings
With this approach, the lab delivered the method to repair vehicle parts that would have cost hundreds of thousands of dollars to replace. “A very expensive part on an aircraft that has experienced some corrosion or wear may cost $400,000; however, you can repair it with cold spray for a fraction of the cost—probably around $2,000,” Champagne says.
By 2012, the Corpus Christi Army Depot (Corpus Christi, Texas, USA) used cold spray to repair magnesium gearbox housings. Such repairs led to the restoration of military rotorcrafts, such as the UH-60 Black Hawk, the AH-64 Apache, and the Sikorsky H-53 helicopter.
The Army also used cold spray to make repairs on aluminum castings and access panels possible, which increased the in-service life of aircrafts, such as the U.S. Air Force F-18 fighters and B1-B bombers. In addition, the properties of the cold spray coating ensured that corrosion damage could not debilitate these parts as easily again.
“These types of repairs were unprecedented at the time,” Nardi says. “This technology opened up a huge door for a lot of those parts to be fixed.”
At the moment, more than 4,500 DoD helicopters possess multiple magnesium gearboxes that are highly susceptible to corrosion damage. More than 1,000 Stryker vehicles have also been decommissioned due to wear and tear. Many other critical parts made from aluminum, stainless steel, and titanium face similar vulnerabilities that jeopardize vehicle safety. Cold spray has the ability to repair these parts and return them back into service again, Champagne says.
In all, the Army expects to save an estimate of $23.6 million per year and almost $300 million in total thanks to cold spray, Champagne says. At the center of these repair efforts, the laboratory has established itself as the DoD’s top expert in cold spray technology.
“For all of the high-pressure cold spray work happening at every branch in the military, the Army Research Laboratory is connected to it in one way or another,” Nardi says. “We are highly integrated with most research that’s going on in cold spray across the Department of Defense.”
Future Military Use
So far, DoD has approved over 200 applications of cold spray repairs, with both the Navy and the Air Force beginning to implement this technology into their maintenance operations with assistance from the lab. After years of steady progress, they say high-pressure cold spray could become one of the most valuable tools in the public sector.
“As far as the number of companies that we’ve worked with, they’ve cut across everything from the medical industry to the aerospace industry,” Nardi says. “Lots of different organizations have directly worked with [the laboratory] in order to develop applications that they are either using now or may use in the future.”
Moving forward, ARL says it is continuing to work toward new cold spray enhancements and applications. In addition to testing new blends of materials, the lab has investigated techniques to accelerate the particles with alternate gases to reduce costs even further. Army researchers say they have already demonstrated that cold spray could be accomplished using a liquid system that can offer benefits not available with standard gas methods.
Researchers have also started to explore using high-pressure cold spray as an additive manufacturing process for the three-dimensional (3-D) printing of whole parts from scratch. In one of the earliest applications of this 3-D method, the laboratory created a component for the Patriot missile system that still exists in the system.
“Cold spray is more than just repair,” Champagne says. “You’re going to see it used as an additive manufacturing process, producing parts for numerous industries, including nuclear power, electronics, automotive, shipbuilding, and the petrochemical industries.”
According to Champagne, current cold spray applications being transitioned by the laboratory include the development of wear-resistant coatings for gun barrels and the repair of high hard armor.
Source: U.S. Defense Video Imagery Distribution System, www.dvidshub.net.
Reference
1 “Cold Spray Gains Momentum as Army's Ultimate Repair Technique,” U.S. Defense Visual Information Distribution Service, June 2, 2020, https://www.army.mil/article/234430/future_army_vehicles_could_see_an_improvement_in_structural_materials (June 18, 2020).