Superplasticity May Work Better In Smaller Packages

April 21, 1999

A physical quality called superplasticity lets manufacturers fashion metal into strong, intricate shapes, such as turbine blades and aircraft components. But achieving superplasticity typically requires impractically long cooking times or high heats. Now researchers at the University of California, Davis, report findings that could simplify that process.

Manufacturers presently are limited to using materials, such as aluminum alloys, that can reach superplasticity -- the ability to stretch a long way without breaking -- at temperatures no higher than 1,800 degrees F. The new experiments brought that temperature down to 450 degrees F. for the aluminum alloy and to 660 to 1,200 degrees F. for other materials that are desirable but currently impractical, such as nickel and a nickel-aluminum alloy.

The results, from the laboratory of Amiya Mukherjee, a UC Davis professor of materials science, are reported in this Thursday's issue of the journal Nature.

The key to cooler superplasticity was switching from materials made of microcrystals to those made of nanocrystals, which are 1,000 times smaller. (Microcrystals range from one to about 20 microns in diameter; 20 microns is about one-fourth the width of a human hair.) The finished nanostructured materials were also much stronger than microstructured ones, said Sam McFadden, the lead author of the Nature paper and a Mukherjee graduate student.

Interestingly, the underlying mechanical changes that occurred in response to stretching and heat in the nanostructured materials were not the same as those known to occur in micromaterials, McFadden said. "There are differences in behavior that the formulas didn't predict."

The authors of the Nature paper, besides McFadden and Mukherjee, are Adjunct Assistant Professor Rajiv Mishra and two researchers at the Ufa State Aviation Technical University in Ufa, Russia, who provided nanostructured materials for the experiments -- Alexandre Jiliaev and Ruslan Valiev.

The research was funded by the U.S. National Science Foundation and the U.S. Civilian Research and Development Foundation for the Independent States of the former Soviet Union.
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