X-Message-Number: 24600
Date: Wed, 8 Sep 2004 05:12:39 -0700 (PDT)
From: Doug Skrecky <>
Subject: Is metallic glass research relevant to cryopreservation?

[Check out the last paragraph about golf club heads.]

Metallic Glass: Material Of The Future?
Hopkins researcher draws on science and 'alchemy' to make new alloys

Mention "glass," and a window pane comes to mind. But under certain
conditions, a metal can also form as a glass, possessing properties that
make it ideal for electric transformers, golf clubs and other products.
Making useful metallic glasses is tricky, but a Johns Hopkins University
researcher has taken on the challenge. Todd Hufnagel is trying to produce
new metallic glasses in bulk form with superior strength, elasticity and
magnetic properties.

In doing so, Hufnagel hopes to learn more about the microscopic events
that occur when molten metal cools into a solid. This is the critical
period when a metallic glass is born.

To scientists, a glass is any material that can be cooled from a liquid
to a solid without crystallizing. Most metals do crystallize as they
cool, arranging their atoms into a highly regular spatial pattern called
a lattice. But if crystallization does not occur, and the atoms settle
into a nearly random arrangement, the final form is a metallic glass.

Window glass possesses this same random atomic arrangement, although it
is not metallic. Unlike window panes, metallic glasses are not
transparent, yet their unusual atomic structure gives them distinctive
mechanical and magnetic properties. Unlike window glass, metallic glass
is not brittle. Many traditional metals are relatively easy to "deform,"
or bend permanently out of shape, because their crystal lattices are
riddled with defects. A metallic glass, in contrast, will spring back to
its original shape much more readily.

"If you rank materials for how springy they are, metallic glasses are off
the chart," says Hufnagel, an assistant professor of materials science
and engineering. "They're far and away better than anything else out
there."

Hufnagel, whose studies are funded by the National Science Foundation and
the U.S. Army Research Office, has set up a lab at Hopkins to test new
alloys. He is trying to create a new metallic glass that will remain
solid and not crystallize at higher temperatures, making it useful for
engine parts. The new metallic glass may also have military applications
as armor-piercing projectiles. Unlike most crystalline metal projectiles,
which flatten into a mushroom shape upon impact, Hufnagel believes the
sides of a metallic glass head will sheer away on impact, essentially
sharpening the point and providing more effective penetration.

His work follows in the footsteps of scientists throughout history who
have stirred together ingredients, trying to make valuable new materials.
"Metallurgy has a long tradition of being a 'black art,'" says Hufnagel.
"For a long time, people did things because they knew they worked, without
understanding why. The real contribution of metallurgy is in starting to
figure out why things work and how we can make them better.

"Part of what we're doing is still sort of alchemy, mixing up new
combinations to see how well they form a glass. But the other part of
this is science. We want to know how the crystallization works, what's
going on there. If you can understand how the crystallization happens,
then, presumably, you can design your alloy to avoid it. There's a lot of
basic research to be done on this stuff."

Because they lack crystal defects, iron-based metallic glasses are very
efficient magnetic materials. And like window glass and plastic, metallic
glass softens as it is heated, making it easy to mold into a final shape.

In manufacturing, properties like these can have great appeal. But making
a metallic glass in thick, bulk form is not easy because most metals rush
to crystalize as they cool. To make a glass, the metal must harden before
the crystal lattice has a chance to form. To create a glass from a pure
metal, such as copper or nickel, one would have to cool it at about 1
trillion degrees Celsius per second, Hufnagel says. That's impractical.

In the 1950s, however, metallurgists learned how to slow the
crystallization by mixing certain metals, such as nickel and zirconium.
When thin layers of such alloys were cooled at 1 million degrees Celsius
per second, they formed a metallic glass. Because of the rapid cooling
requirement, this material could only be made as a thin ribbon, a wire or
a powder.

More recently, however, scientists have created about a dozen metallic
glasses in bulk form--bars, for example--by mixing four or five elements
that possess atoms of varying sizes. That makes it tougher for the
mixture to form crystal lattices. One of these new metallic glass alloys
is being used commercially to make powerful golf club heads.

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