nesium need heat treatment to improve strength, which is nano-scale precipitation from the age hardening process,” he said. “Nanoparticles strengthen in the same way. But heat treatment takes a long time and high temperature. Solving that [with nanoparticles] would be significant.” The general rule is nanoparticles
can give aluminum and magnesium the strength of gray iron along with slightly higher elongation. At the same time, ductility and toughness are unaffected. “Nanotechnology gives us what I call
a free lunch,” said Robert Hathaway, vice president of materials and pro- cesseses for Oshkosh. “We can increase our mechanical properties without reducing the ductility or toughness of the material. The particles are so small, machinability should still be good.”
Means to an End One of the earliest challenges of us-
ing nanotechnology in metalcasting was finding a way to uniformly disperse the minute pieces of material throughout the metal. The tiny particles are drawn together by van der Waals force (an attractive or repulsive force among molecules) and tend to stick together in clumps. The attractive force is so high, keeping the particles apart in order to allow the aluminum or magnesium to bond with them takes a lot of energy. The nano research team’s eureka
moment came when it found that us- ing ultrasonic waves was effective in keeping the nanoparticles apart and uniformly dispersed throughout the metal during solidification. “For the past six years, we’ve been
Nanoparticles’ appeal is that they can give specific properties to certain materials. The nanoparticles in this illustration are tuned to optimize their magnetic properties. Their dis- covery could lead to a low-cost technology for cleaning arsenic from drinking water.
high strength, found in materials at the nano-scale while maintaining the properties inherent in the bulk material. With in-kind funding from Eck, Osh- kosh Corp., Oshkosh, Wis., the Univ. of Wisconsin-Madison, Nanostructured & Amorphous Materials Inc., Houston, and the American Foundry Society added to the nearly $5 million from TIP, the nano project is estimated to cost $10 million through Jan. 31, 2015. But as one of the tenets of TIP implies, risking those fund could yield great rewards. According to Weiss, increases in
MODERN CASTING / March 2010
strength of between 100 and 120% have been accomplished using 2% volume fraction of nanoparticles in metal matrix composites. “Obvious applications are going to
be in the transportation market, like military, aerospace and commercial cars,” Weiss said. “With the mechanical improvements, you can design parts significantly lighter.” Li compares the strengthening of
the alloy with nanoparticles to that of strengthening via heat treatment. “Traditionally, aluminum and mag-
working on the fundamentals of how to get the nanoparticles to disperse in the metal,” Li said. “Ultrasonic technology is one of the more inexpensive ways.”
Lab to Line Current nanotechnology testing has
been performed with batches of 5 to 10 lbs. of material at a time. In order to use the process in a metalcasting facility, more work is required. “How do we scale up to reasonable
production batches of material, which at Eck is 500 lbs.?” Weiss said. “The whole jist of the TIP money is to be able to scale it up to make real components. The plan is to take it from a laboratory curiosity into something with which we can make metal castings.” To scale up the work, tools to disperse nanoparticles on a larger scale have to
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Photo courtesy of Rice Univ. Public Affairs/News and Media Relations
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