Superplasticitythe ability to stretch a material extensively without breaking it or damaging its mechanical propertieshas only been possible to achieve in many materials by heating them at extreme temperatures for long periods of time. Researchers at the University of California (UC; Davis, CA; 530-752-1776) have now found a way to reduce the required temperature by more than 1300°F by using nanocrystals instead of microcrystals. The development, which also makes the materials stronger, is key for manufacturing aircraft components and other structures.
How It Works (Back to Top)
The researchers found that the key to reducing the required temperature for superplasticity was in switching from materials made of microcrystals to those made of nanocrystals, which are 1,000 times smaller. In addition to reaching superplasticity at lower temperatures, the finished nanostructured materials are much stronger than the microstructured ones. This is true for metals, alloys, and ceramics. The research was conducted by UC graduate student Sam McFadden under the direction of Amiya Mukherjee, a UC Davis professor of materials science.
"Interestingly, the underlying mechanical changes that occurred in response to stretching and heating in the nanostructured materials are not the same as those known to occur in micromaterials," McFadden says. "There are differences in behavior that the formulas didn't predict." Additional research is being pursued.
Applications (Back to Top)
Manufacturers presently are limited to using materials such as aluminum alloys that can reach superplasticity at temperatures no higher than 1,800°F. The new experiments brought that temperature down to 450°F for the aluminum alloy. The temperature was also reduced to 660 to 1,200°F for other materials that are desirable but currently impractical, such as nickel and a nickel-aluminum alloy.
Because of this research, manufacturers will be able to utilize a broader range of materials at a lower production cost. The new materials will be used to fashion metal into strong, intricate shapes such as turbine blades and aircraft components.
The research is reported in the April 22, 1999, issue of Nature. McFadden was lead author on the paper. Additional authors included Mukherjee, adjunct assistant professor Rajiv Mishra, and two researchers at the Ufa State Aviation Technical University (Ufa, Russia) who provided nanostructured materials for the experimentsAlexandre 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.
For more information, call Amiya Mukherjee of UC Davis at 530-752-1776.