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The Next Big Thing:
Studying Properties of Nanostructured Materials

Materials scientists have worked with metals like copper and nickel for many years, so the properties of these materials are well documented. But the availability of nanostructured versions of these familiar metals opens up possibilities for new and unique combinations of mechanical properties – and a whole new research frontier.

Studying nanostructures requires a new set of test equipment. Researchers using a diamond indentation tester to study the fracture toughness of nanofibers produced these images showing damage to silicon carbide fibers. (Larger JPEG version, top - 125k)   (Larger JPEG version, bottom - 122k)

Nanostructured materials result from novel processing techniques that dramatically reduce the size of crystals that make up the bulk metals, dropping them from the micrometer- to nanometer-size scale. That alters the behavior of line defects in the crystalline structure known as dislocations, making the nanostructured metals orders of magnitude stronger than their traditional forms.

But even in the nanoworld, there is no free lunch. The strength increase may come at the cost of other important properties, a trade-off that provides an important new area for research.

"If you look at the performance of a metal in an aircraft, strength is only one of the properties that we care about," says Ashok Saxena, chair of Georgia Tech's School of Materials Science and Engineering. "It's also important to get the right amount of toughness, creep resistance, corrosion resistance and fatigue resistance. We don't know yet if these new materials will be optimal in all those properties."

The new nanostructured materials are also expensive, too costly to study using traditional test procedures. So researchers are developing new nanoscale testing techniques to investigate key properties using only small samples.

For example, Georgia Tech researchers use a diamond nanoindentation tester to study deformation and hardness properties of the new materials. The device presses a diamond tip just 10 nanometers wide into the sample under study. The force required to make the indentation and the total displacement of the tip together provide data useful to understanding the properties.

Atomic force microscopy also provides information about the new nanostructured materials. By furnishing a topographical view of the materials' surface, researchers can "see" features 3 to 5 nanometers high that provide evidence of metal fatigue. They also plan to modify the stage of a scanning electron microscope to obtain visual confirmation of the information obtained during deformation testing.

Saxena adds, "There is good reason to be optimistic about these new materials, but there is good reason to be cautious."

For more information, contact Ashok Saxena, School of Materials Science and Engineering, Georgia Tech, Atlanta, GA 30332-0245. (Telephone: 404-894-2888) (E-mail: ashok.saxena@mse.gatech.edu)