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Atomic Bonding from a Bottle? These Scientists Use Supersonic Spray to Repair Turbines

Two years ago, scientists at the GE Global Research labs (GRC) in upstate New York found a futuristic way to fix things: blowing metal powder, at four times the speed of sound, onto parts in need of service. “The tiny bits of material fly so fast then they essentially fuse together when they hit the target,” says Gregorio Dimagli, materials scientist from Avio Aero. “Unlike welding, you don’t need to apply heat to make them stick. The bond happens on the atomic level. That’s why we are so excited.”

This is a big deal. The method, called cold spray, will allow Avio Aero and its parent, GE Aviation, to repair turbine and compressor blades without changing their highly complex underlying crystal structure. “Manufacturers spend a lot of time to make the part just right,” Dimagli says. “But when you heat up metal and then cool it again, it changes in the same way powder snow can become a sheet of ice after a warm spell.”

Dimagli and his team just partnered with the Polytechnic University of Bari, Italy, to perfect the applications of cold spray, sometimes also called “3D painting,” as well as laser deposition and other additive manufacturing techniques.

Top: Unlike traditional manufacturing, which removes material to achieve the final shape, most additive methods build parts from the ground up. This GIF captures particles leaving the cold spray nozzle at four times the speed of sound and hitting their target. The image was slowed down by using a camera capable of shooting 10,000 frames per second. Above: GE reached out to the Slo Mo Guys to explain cold spray. GIF credit: GE Global Research.

The new lab will employ three Avio Aero scientists and six researchers from the university. They will use thermography and other scientific disciplines to look for the best applications of the new methods.

Anteneh Kebbede, manager of the Coatings and Surface Lab at the GRC that helped developed cold spray, says the technology is “like a fountain of youth for machine parts.”

3D painting deposits metal powder flying at velocities of up to Mach 4 on precise models to produce and repair jet engine blades, rotors and other components without resorting to machining or welding.

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He says the method can build whole new parts with walls as thick as one inch or more. “For manufacturers the potential benefits are enormous,” Kebbede says. “Imagine being able to restore an aging part to its original condition with a tool that looks like spray gun.”

The 3D painting gun uses pressurized carrier gas zipping through a de Laval nozzle to accelerate powder particles as small as 5 microns to supersonic velocities. The speed causes localized high energy collisions when the particles hit the surface, the micro version of bullets hitting a steel bar. “Powder particles slam into the surface and form a diffusion bond with the part,” Kebbede says.

Cold spray operators are using a computer-controlled robot to manipulate the gun. Like 3D printers, the computer works with a 3D image of the part. Engineers program the robot so that it moves in an optimal way to deposit the powder. “All the hard work is in the details,” Kebbede says. “The powder selection, the conditions the powder experiences in the gun, the speed of the gun, the gun distance from the part and its angle relative to the part are just some of the inputs that lead to a good bond. That’s the trick. The same process that can cause build up can also cause erosion.”

Dimagli says that possible applications range anywhere from heavy-duty gear boxes for oil and gas machinery, to gas turbine rotors and jet engine blades. “These methods are the future,” he says. “Compared to what we are using now, you get better quality for less money and you are also done faster.”

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