In a counterintuitive discovery by MIT researchers, metals struck by objects at super high velocities increase in strength with rising temperatures, reversing the usual softening effect seen under normal conditions. This new understanding, based on experiments using tiny sapphire particles shot at metals, could revolutionize material designs for extreme environments such as spacecraft shields or high-speed manufacturing processes.
Caption:MIT scientists discovered that when metals are deformed at an extreme rate by an object moving at high velocities, hotter temperatures make the metal stronger, not weaker. Here, 3 particles are hitting a metallic surface at about the same velocity. As the initial temperature of the metal is increased, the rebound is faster, and the particle bounces higher because the metal becomes harder not softer, too.
The tiny particles they used were made of alumina, or sapphire, and are “very hard,” Dowding says. At 10 to 20 microns across, these are between one-tenth and one-fifth of the thickness of a human hair. When the launchpad behind those particles is hit by a laser beam, part of the material vaporizes, creating a jet of vapor that propels the particle in the opposite direction.
The surprising effect appears to result from the way the orderly arrays of atoms that make up the crystalline structure of metals move under different conditions, according to the researchers’ analysis.
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