Science of splat

Like a bug that crashes into and sticks on your windshield, particles of metal stick to surfaces on aircraft engine components when propelled at speeds of 500 to 1,500 meters per second. Re-searchers at Sandia National Labs are studying what happens when metals, alloys, and ceramic blends measuring 10 to 15 microns smack into engine components in a process called cold spray. Unlike thermal sprays that re-quire preheating the particles into a semi-molten state, the new cold spray process works at room temperature. Cold-sprayed materials typically re-main at room temperature until slamming into a substrate, which the researchers believe helps the metal particles form tight bonds. The disadvantage with semi-molten materials is that when they cool, they create residual stresses that cause defects later. The researchers think the cool process is better because the high-velocity impacts disrupt the metal oxide films on the particles and substrate surfaces, pressing their atomic structures into one another. "Cold-sprayed coatings have a higher density and smoother finishes than traditional thermally sprayed coating's," says Sandia researcher Mark Smith. "The electric properties tend to be better too." Smith notes that the Sandia team is still characterizing the coatings other properties. Sandia is currently working with a consortium of eight U.S. companies in an effort to improve the technique. Additional applications for the process include depositing coatings and conductive metals onto automotive components, building components layer by layer, and joining chemically dissimilar materials together as an alternative to welding. For more information, go to www.sandia.gov.