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Ames Lab studies processing methods

Most materials scientists follow tried-and-true methods for melting, cooling, and shaping various materials into usable forms even though the science behind those methods is not always fully understood. An effort is underway at the Materials Preparation Center (MPC), part of the U.S. Department of Energy's (DOE) Ames Laboratory, to delve more deeply into the mysteries of processing science—the methods by which metals, alloys, polymers, and ceramics are synthesized to give them specific properties. Ames Lab scientists hope to understand existing processing methods better and develop techniques for making advanced materials for future technologies.

A new program called the Process Science Initiative (PSI) offers a limited pool of competitive funding for two types of materials-processing projects: those that lead to an improved fundamental understanding of existing processing techniques, and those that explore new techniques for producing novel materials. The DOE provides funds for the PSI program; MPC and Ames Lab provide the research facilities. The MPC is a designated DOE national user facility that specializes in preparing small samples of high-purity, novel materials that are not available from commercial sources.

It is critical that scientists understand what happens to a material when it goes from a liquid to a solid state because most metals and alloys are made of tiny crystals. The way in which the liquid crystallizes to form the microstructure of the solid determines the material's properties, such as its strength and formability. Subsequent secondary processing, such as rolling or extruding, also affects a material's properties.

"In a lot of the recent research, we've focused heavily on the properties of materials without really understanding how we arrived at, or control, the microstructure," said Brian Gleeson, Assistant Professor of Materials Science and Engineering at Iowa State University and PSI Program Manager. "Materials scientists see the need for research that will give them this type of information."

Larry Jones, Director of the MPC, said determining how to synthesize metals and alloys is a difficult task. "The materials we're dealing with today often have high melting points, or they may easily pick up impurities from the crucibles we melt them in," he said. "And they may need to be cooled in a very regimented way to produce the desired microstructure."

With most complex materials, scientists have a limited understanding of what happens to the metal or alloy while it's being processed. "You have to know the conditions—such as the temperatures, forces, and amount of deformation—affecting that material during processing," Jones said. "Accurately measuring those parameters is not easy when you're dealing with temperatures of 1800°C (3300°F), which is an aggressive thermal environment."

The PSI program is the only known initiative to focus specifically on improving the science of materials processing, according to Gleeson. In fiscal year 2000, four projects received $141,000 in PSI funds. The DOE authorized an increase of the PSI budget to $250,000 for the current fiscal year, which began October 1. Four projects have already been selected to share approximately $175,000 of those funds, with the remaining $75,000 to be allocated later in the year.

Among the projects receiving PSI funds is one in which Ames Lab scientists are studying the properties of liquid/solid interfaces. "In alloy systems, there's a range of solidification where the liquid and solid phases of the material coexist," Gleeson said. "It's the coexistence of the solid and the liquid that really sets the stage for the final product."

The scientists built a rig that enables them to reach and maintain the liquid/solid coexistence and then measure the properties of the interface between the two phases. "This is very fundamental knowledge that could be applicable to a range of other alloy systems," Gleeson said.

Another project that received funding for the current year involves synthesizing and characterizing polymer gels that respond to pH or temperature changes. The goal is to develop polymer gels that would either swell or contract in response to specific pH or temperature changes. "This is a formidable materials-synthesis challenge, but success would be of both fundamental and practical significance," said Gleeson.

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