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US Army embracing cold spray to battle corrosion damage

Stryker AFV
Soldiers mount a Stryker vehicle during zone reconnaissance training in 2019. Photo: US Army

The US Army is making progress on a technology that would provide it with a capability to quickly repair damage to its assets and protect them against corrosion.

For a long time, the US defense department had to decommission countless 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 US Army about $1.2 billion.

The Stryker armored fighting vehicle, for example, possesses a highly sophisticated armor system that protects the vehicle from all kinds of ballistic threats, from artillery fragments to rocket-powered grenades; however, even light corrosion damage built up over time can penetrate its defenses and require serious repair.

But now, researchers at the US Army Combat Capabilities Development Command’s Army Research Laboratory have refined a repair technique known as high-pressure cold spray to the point where it has become the military’s ultimate solution to corrosion damage and dimensional restoration.

“This is a repair technology that has been a godsend to the Department of Defense,” said Dr. 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 for the Navy, the Air Force, the Marines and the Coast Guard.”

Cold Spray as a tool in corrosion prevention

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,” said Aaron Nardi, team lead of the laboratory’s Cold Spray Center. “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.”

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 Dr. Anatolii Papyrin, an early Soviet Union pioneer of cold spray technology in collaboration with Sandia National Labs.

Champagne and his colleague Dr. Dennis Helfritch, along with the South Dakota School of Mines, designed their own cold spray system based upon the needs of the DOD and industrial base and 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 emerged as the commercial producer of the system in 2012.

Improvements to the system were made from research partners with ARL including the United Technologies Research Center and the Pennsylvania State University. The VRC system far exceeded the performance of its predecessors.

Over the past 20 years, Army researchers identified thermal treatments, particle size optimization and multiphase powder formulations, which 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 under all circumstances. Army researchers developed every aspect of powder synthesis and production, even 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 producing cold spray powders commercially.

With this approach, the lab delivered the method to repair highly valuable vehicle parts that would have costed 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 said.

By 2012, the Corpus Christi Army Depot 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 said. “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. Countless 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 said.

The Army expects to save an estimate of $23.6 million per year and almost $300 million in total thanks to cold spray, Champagne said. At the center of these repair efforts, the laboratory has established itself as the DOD’s foremost 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 said. “We are highly integrated with most research that’s going on in cold spray across the Department of Defense.”

DOD has approved over two hundred applications of cold spray repairs so far. Both the Navy and the Air Force have also started to implement this technology into their maintenance operations with assistance from the lab. After years of growing progress, high-pressure cold spray may prove to become one of the most valuable tools in not just the DOD but also 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 said. “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.”

Researchers continue to work toward new cold spray enhancements and applications to aid the warfighter.

In addition to testing new blends of materials, the lab has investigated techniques to accelerate the particles with alternate gases in order to reduce costs even further. Army researchers have already demonstrated that cold spray could be accomplished using a liquid system that can even offer additional benefits not available with standard gas methods.

Researchers have also started to explore high-pressure cold spray as an additive manufacturing process to 3-D print whole parts from scratch. In one of the earliest applications of this 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 said. “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 high wear resistant coatings for gun barrels and the repair of high hard armor.

With so much potential in store, Champagne said, cold spray technology and its numerous applications demonstrate a lot of promise for the near future.