For release: March 26,1999
Contacts:
Bill McCallum, Metallurgy and Ceramics, (515) 294-4736
Matt Kramer, Metallurgy and Ceramics, (515) 294-0276
Susan Dieterle, Public Affairs, (515) 294-1405
AMES, Iowa -- Researchers at the U.S. Department of Energy's Ames Laboratory now have a
better understanding of the solidification process of neodymium-iron-boron permanent
magnets and the role of alloying additions.
This knowledge represents a fundamental breakthrough in understanding how the magnetic
material forms, the researchers say, and may aid manufacturers in producing smaller,
stronger magnets.
A magnet's performance hinges on the size and alignment of its individual crystals, known
as the microstructure, said Bill McCallum, a senior metallurgist at Ames Laboratory. In
order to strengthen the magnets, it is necessary to control their microstructure.
"For many years, we've known that in order to enhance the properties in these
magnets, specific processing steps had to taken. This typically involved adding extra
elements and heat-treating the alloy," McCallum said. "What we haven't known,
though, is why those steps enhanced the microstructure, which in turn improves the
magnetic properties."
McCallum, together with scientists Kevin Dennis and Matt Kramer, studied the
solidification process in hopes of answering that question. Their research resulted in the
discovery of key aspects that control the microstructural development of Nd-Fe-B magnets,
the most widely used permanent magnets.
Kramer said the discoveries are a breakthrough in the fundamental understanding of how
peritectic alloys, such as Nd-Fe-B, form. Peritectic alloys are materials which, during
cooling, form a mixture of a solid and a liquid before completely solidifying, Kramer
said.
Solidification in peritectic alloys normally results in large-scale phase segregation,
producing unwanted compounds that degrade the magnetic properties. Certain alloy additions
altered the solidification by making it easier to form the right microstructure without
additional heat treatments. Further study into the phenomenon of the solidification
process showed that certain events happened under a very narrow range of quenching
conditions, Kramer said.
Using a process known as melt-spinning, the researchers could form highly textured samples
over a small range of wheel speeds (10-15 meters a second). Increasing or decreasing the
speed beyond those parameters produced a very different microstructure, Kramer said.
Additions of titanium-carbide altered the solidification kinetics, changing how and at
what temperature certain compounds formed.
"Knowing the physics and chemistry that control the process, we can now more
intelligently choose additions to select the desired outcome," Kramer said.
This research has been carried out in collaboration with two other Department of Energy
laboratories -- Idaho National Engineering Laboratory and Brookhaven National Laboratory
-- and has received several honors, including a 1997 R&D 100 Award. The research has
also spawned interest in hard magnetic materials at other national laboratories in
conjunction with the Center for Excellence in Materials Synthesis and Processing under the
DOE's Basic Energy Sciences program.
While the DOE laboratories have focused on the fundamental understanding of
microstructural development, the results from this research have enabled industry to
develop alloys requiring fewer processing steps to optimize the magnetic properties,
reducing their costs and saving energy.
Ames Laboratory is operated for the DOE by Iowa State University. The Lab conducts
research into various areas of national concern, including energy resources, high-speed
computer design, environmental cleanup and restoration, and the synthesis and study of new
materials.
Last revision: 4/13/99 sd