“The work is promising,” says Anders. “We have conceived, designed and demonstrated scalable prepregging methods.” Now the researchers are pivoting their efforts to transition the technology from the lab into commercial products.
Next Generation Military Applications
Project: Cold spray processes for polymers and composites
School: Rowan University
Location: Glassboro, N.J.
Principal Investigators: Francis Haas and Joseph Stanzione, III
Researchers at Rowan University are leading a project to pioneer cold spray of polymers and composites for potential use in next-generation military applications. The five-year, $14.5 million dollar project is a collaborative effort with the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory (CCDC ARL), the Kostas Research Institute (KRI) at Northeastern University, Clemson University, Drexel University, University of Massachusetts Amherst and PPG Inc.
Cold spray processing involves spraying of powdered material at extremely high velocities, generally hundreds of meters per second. When the sprayed particles make contact with the substrate, they flatten out and can chemically and mechanically interlock with the structure. Despite its name, cold spray is anything but cold. As Francis “Mac” Haas, Rowan University assistant professor of mechanical engineering explains, “You can get a cold spray that starts off at 700 degrees Celsius – so it is in no way cold – but it’s cold relative to its melting point.”
While cold spray processes are well-developed for metals, they represent a new frontier for polymers and composites. Adapting the technology involves several fundamental challenges. For polymers, the processing temperatures are much lower (generally between 70 and 200 degrees Celsius) and are likely to be governed by the glass transition temperature of the sprayed polymeric material.
In addition, polymers can become tacky when heated, which hinders flow for spraying. Polymers also react differently when they impact the surface. For example, deposition efficiency rates for polymers – the amount of sprayed powder that “sticks” to the substrate – are generally quite low. “You get a tiny amount of powder to stick, and even then, that doesn’t necessarily mean it will do a particularly good job, whether structurally or as a coating. That just means it’s stuck to the wall,” says Haas. “So there’s a lot of basic science that needs to be done.”
Cold spraying processes for polymers and composites are expected to enable the manufacture of functionally-graded composites that have different materials layered into the same part. Researchers believe that by changing the powder mixture they can create varied composite layers with different resins, fibers and fiber-to-resin content. Joseph Stanzione III, associate professor of chemical engineering and founding director of the Advanced Materials & Manufacturing Institute (AMMI) at Rowan, says that the layers could be made from a variety of materials, including polymer-on-polymer, polymer-on-metal or metal-on-polymer. “That’s the beauty of this project!” he says.