[TheForge] 'glassey' steel

[Carlton McKenney]

Came across this on the Knife forum :

Dear knife enthusiasts,
I thought this could spike your interest :-)
Bjoern
Published online: 25 June 2004; | doi:10.1038/news040621-8
Recipe unearthed for 'glassy' metal
Philip Ball
Sturdier steel forged using rare element.
An extraordinary type of steel has been invented
that is more like glass than metal. It is
unusually strong, and its developers hope it could
be used to build tougher medical implants or
lighter aircraft.
"People have been trying for decades to make these
materials," says Zhao Ping Lu of Oak Ridge
National Laboratory in Tennessee. Lu and his
colleagues have finally succeeded in finding the
right recipe for keeping steel 'glassy' as it
freezes1.
In normal metals, the atoms are packed together in
an orderly, "crystalline" manner, like oranges on
a fruit stall. But in amorphous solids, like
glass, the atoms are disorderly; they resemble
atoms in a liquid, except that they are more or
less frozen in place.
Metals with this jumbled atomic structure are
typically harder and stronger than their
crystalline counterparts, so they are very
attractive to engineers. For example, these
amorphous alloys could be used to build aeroplanes
that are as strong as those made from regular
metals, but that use less material, making them
much lighter.
Steel deal
The problem is that amorphous metal alloys are
generally very expensive. Those on the market are
composed mostly of costly zirconium or palladium.
An amorphous version of steel, based on iron,
would reduce the price considerably.
"All the elements we use in our alloys are cheap,"
Lu says. He estimates that his glassy steel could
reduce the price tag of amorphous metals from $220
a kilogram to less than $33 a kilogram.
That is still pricey compared with ordinary steel,
so it is unlikely that amorphous steel will be
holding up buildings in the near future. Instead,
it will probably be used for specialized
applications such as tough coatings for industrial
machinery, sporting equipment such as tennis
racquets and golf clubs, and robust medical
implants.
Crystal clear
People have made amorphous steel before, but only
in small quantities. If it is cast into blocks
bigger than about 4 millimetres across, parts of
the alloy tend to crystallize, reducing its
strength and hardness.
Lu and colleagues have discovered how to avoid
this problem. The key is to find the right
elements to blend with iron. Steel is basically a
mixture of iron with small amounts of carbon, but
most industrial steels contain a sprinkling of
other elements, such as chromium, which is found
in stainless steel.
The researchers used a mixture of iron with
chromium, manganese, molybdenum, carbon, boron,
and, crucially, the rare metal yttrium. Alloys
containing around 1.5% yttrium can remain molten
at substantially lower temperatures, which helps
the amorphous structure to remain in place as the
metal solidifies.
Yttrium also slows down the growth of crystals of
iron carbide, which otherwise appear as the alloy
cools and encourage the steel to become
crystalline throughout. So far, Lu's team has made
metal bars 12 millimetres wide, but that is just
the largest size their lab technique can manage.
"I think we can get bigger than that," says Lu.
Amorphous steel has one more beneficial property:
unlike ordinary steel, it is not attracted to
magnets unless it is cooled to low temperatures.
Lu says that there are important military
applications for such 'non-magnetic' steels, but
for now they are being kept firmly under wraps.
References
1. Lu, Z. P. , Liu, C. T., Thompson, J. R &
Porter, W. D., Mazzafera,P. & Fazuoli, L. C. .
Physical Review Letters, 92, 245503,
10.1038/news0400621-8(2004).

--------------------------
They that can give up essential liberty to purchase a little
temporary safety deserve neither liberty nor safety.
--Benjamin Franklin--


Carlton

All that is gold does not glitter and
not all that wander are lost.

Tolkein