For release: Oct. 25, 1999
Contacts:
Bruce Cook, Metallurgy and Ceramics, (515) 294-9673
Alan Russell, Metallurgy and Ceramics, (515) 294-9225
Susan Dieterle, Public Affairs, (515) 294-1405
For technical information on the compound, click here.
AMES, Iowa -- Researchers at the U.S. Department of Energy's Ames Laboratory made a gem
of a discovery while tinkering with an unlikely material -- it's the second-hardest bulk
substance after diamond.
By introducing a small amount of silicon into an alloy of aluminum, magnesium and boron,
they created a material slightly harder than cubic boron-nitride, the material now ranked
second. But the Ames researchers hope that experiments with other additives will make it
even harder.
"We think that by tweaking the composition, we may be able to push the hardness up a
little higher," said Bruce Cook, an associate scientist and lead investigator on the
project. "This was the first additive we tried and it produced a material that's
right up there with cubic boron-nitride. But there may be other variations that could
further increase the hardness
of this material."
Cook and his colleagues tested samples of the alloy on several different instruments, all
of which measured the hardness of the material at approximately 46 gigapascals (the
equivalent of 6.67 million pounds per square inch), slightly higher than cubic
boron-nitride's hardness of about 45 GPa (6.53 million psi). By contrast, diamond's
hardness is estimated at between 70 and 100 GPa (10.15-14.5 million psi).
The aluminum-magnesium-boron compound could also be the least expensive of the three
materials. Cook estimated its cost at around $700 per pound, compared to cubic
boron-nitride's price tag of up to $7,000 per pound and diamond's cost of $2,000 per
pound. That could mean huge savings for manufacturers that use these types of materials in
abrasives and cutting tools for grinding and machining applications.
"The fact that industries are willing to pay that price for cubic boron-nitride gives
some insight into what a critical industrial process this is," said Alan Russell, an
Ames Lab associate scientist and an associate professor of materials science and
engineering at Iowa State University. "Cutting iron and steel is an enormous part of
the U.S. manufacturing economy."
Cook said diamond isn't an option for cutting and grinding steel because it reacts by
turning into graphite when brought into contact with iron-based materials at high
temperatures. In the high-speed grinding that takes place in the auto industry, for
example, friction between the steel and the tool produces surface temperatures as high as
1000 C (1800 F).
Cubic boron-nitride doesn't have the iron reactivity problem, but it's costly because it
is produced at extremely high temperatures and pressures. "It requires pressures of
50,000 atmospheres," Russell said. "That's similar to what you would encounter
100 miles deep into the earth."
Cook said preliminary tests indicate that the Ames Lab compound doesn't react with iron
the way diamond does. A Michigan company that manufactures tools, dies and molds for the
automotive industry tested samples of the material and reported favorable results. Cook
said the company was especially pleased that the material didn't fracture -- a common
problem for many brittle, abrasive materials.
Cook discovered the hardness of the aluminum-magnesium-boron compound by accident. He was
researching its thermoelectric properties in 1992 when he discovered that he couldn't cut
the samples he'd made. "We have high-speed, precision diamond saws in the lab that
can cut virtually anything, and we weren't able to cut this material," Cook said.
"That
caught our attention."
Russell noted that although the material has been around for awhile, its mechanical
properties were never investigated. "When Bruce discovered the hardness, it was
unexpected and something that no one had thought to look for previously," he said.
It is also an unlikely candidate for a hard material because of the structure of its unit
cell, or fundamental building block. "A diamond has eight carbon atoms in a unit
cell. It's a very simple, highly symmetric structure," Russell explained. "This
material has 64 atoms in the unit cell. If you gave this structure to a panel of experts
and asked if it would be hard, they'd say, 'Nah, the crystal structure is all wrong.' But
it's extremely hard. And that's the kind of thing that gets scientists salivating."
Cook said the complex chemical structure makes it possible to enhance the compound's
hardness by substituting other elements, such as silicon. "We thought we could change
the bonding environment if we added silicon to the structure, and it worked. It made the
material harder," he said.
During 1998, the scientists used a one-year Department of Commerce grant from ISU's Center
for Advanced Technology Development to study the material and possible additives to
enhance its hardness. They also received a small grant through the Roy J. Carver
Charitable Trust. Currently, the researchers are looking for additional funding for a more
extensive study of the material's preparation and properties.
Among their research priorities are a better scientific understanding of the material
itself and figuring out the best, most inexpensive way to produce large quantities of the
compound. They also want to investigate the possibility of producing the material as a
uniform powder that could be deposited as a wear-resistant coating on surfaces such as
bulldozer and snowplow blades. "We know that the two other hardest materials won't
tolerate it," Russell said. "This one might."
The researchers, along with assistant scientist Joel Harringa, have submitted a paper on
their findings to Scripta Materialia, a peer-reviewed materials journal, and have applied
for a patent.
Ames Laboratory is operated for the Department of Energy by ISU. 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.
Return to News
Release index
Last revision: 11/29/99 dbm
Home | Disclaimer