A cold spray process, where metal powder is blown at four times the speed of sound on to parts, is being researched by scientists from Avio Aero and Polytechnic University of Bari, Italy. The method will allow Avio Aero and its parent, GE Aviation, to repair turbine and compressor blades without changing their highly complex underlying crystal structure.
“The tiny bits of material fly so fast then they essentially fuse together when they hit the target,” stated 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.”
Possible applications range anywhere from heavy-duty gear boxes for oil and gas machinery, to gas turbine rotors and jet engine blades. “Manufacturers spend a lot of time to make the part just right,” added Dimagli. “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.”
The system uses pressurized carrier gas 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 forming a diffusion bond with the part. 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.
Dimagli and his team have just partnered with the Polytechnic University of Bari to perfect the applications of cold spray, as well as laser deposition and other additive manufacturing techniques. 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.