high-temperature, advanced materials, ceramics, metallic, intermetallic compounds

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Abstract, --December 30, 2003-- Researchers at two U.S. laboratories have made progress in the field of advanced materials, developing intermetallic compounds that break traditional rules and ceramics that can withstand extreme temperatures.

Many intermetallic compounds are too brittle to handle, but researchers at the U.S. Department of Energy's (DOE) Ames Laboratory have discovered that intermetallic compounds composed of rare earth elements and other metals are ductile at room temperature.

"You can beat on these new materials with a hammer, and they won't shatter or fracture ... they're that ductile," said Karl Gschneidner, Jr., senior metallurgist at Ames Laboratory.

The new intermetallic materials combine a rare earth element with certain main group or transition metals, resulting in a binary compound with a crystal structure in which an atom of one element is surrounded by a cubic arrangement of eight atoms of the other element. The study has focused on Y-Ag, Y-Cu, and Dy-Cu compounds, but a preliminary examination has shown that Ce-Ag, Er-Ag, Er-Au, Er- Cu, Er-Ir, Ho-Cu, Nd-Ag, Y-In, and Y-Rh are also ductile.

While these new rare earth intermetallic materials could be used to produce corrosion-resistant coatings, flexible superconducting wires, or extremely powerful magnets due to their high-temperature strength and corrosion resistance, Ames researchers hope that studying these materials will also lead to a better understanding of traditional brittle intermetallics.

Researchers atDOE's Sandia National Laboratory have developed ultra-high-temperature ceramics that could be used as thermal insulation materials on hypersonic vehicles such as the space shuttle. The ceramics are composed of zirconium diboride, hafnium diboride, and composites of those ceramics with silicon carbide.

The ceramics are extremely hard and have high melting temperatures (3,245C for zirconium diboride and 3,380C for hafnium diboride) but, in their present state of development, have exhibited poor strength and thermal shock behavior. These deficiencies have been attributed to an inability to make the ceramics fully dense with good microstructures.

Researchers report having created 100% dense, or nearly so, ultra- hightemperature ceramics that have favorable microstructures, as indicated by preliminary electron microscopic examination. In addition, the researchers have hot pressed the ceramics with a wide range of silicon carbide contents. Availability of a range of compositions and microstructures, Sandia says, will give system engineers added flexibility in optimizing their designs.

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