[TheForge] (no subject)

[Clyde Wynia]

But can you forge it?
New amorphous steel is twice as strong


By Charles Choi
United Press International

New York, NY, Jun. 24 (UPI) -- U.S. scientists have made amorphous steel,
which has molecular bonds that resemble those of a liquid more than a metal,
and a hardness and strength more than double the best ultra-high-strength
conventional steels.
The new steel could find use in everything from submarine hulls to
skyscrapers, experts told United Press International.
Steel is a metal alloy composed mostly of iron, with varying amounts of
carbon and other elements, such as titanium. Its molecular structure is
crystalline, containing orderly rows and formations of atoms.
In amorphous substances, the atoms are highly disordered. One example is
window glass, which is more akin to an extremely viscous, immobilized liquid
than a solid. Another amorphous substance is water ice, the most dominant
form of water in the universe, which condenses from water vapor onto cold
surfaces, such as interstellar dust, and forms the deep-space wanderers
known as comets.
Amorphous materials possess "a non-crystalline structure, in which the atoms
arrange randomly, thus no crystallographic defects" form, Zhou Ping Lu, a
research scientist at Oak Ridge National Laboratory in Tennessee, told UPI.
This is why they can be so strong, he added.
Compared with crystalline counterparts, amorphous materials usually show
superior mechanical and temperature properties and corrosion resistance. On
the other hand, amorphous materials can cost about $100 a pound, "much more
expensive than the crystalline materials," Lu said.
Several amorphous, iron-based alloys already have found use in industry. An
amorphous, ferro-magnetic alloy, sold under the trademarked name Metglass,
has extremely high energy-conversion efficiency when used in the cores of
electrical transformers or other energy converters.
"As a result, using these materials as cores can save up to two-thirds of
total energy loss due to heat dissipated by distribution transformers and
motors with conventional ferro-magnetic cores," Lu said.
Because of their strength and anti-corrosion properties, amorphous steel
also would be desirable in buildings, but until now no one has been able to
make components big enough to be structural members. Before Lu and his team
conducted their research, the largest amorphous steel rod anyone had cast
was only about 4 millimeters wide.
Now, after nearly a year of work, the team believes it has found a way to
make amorphous steel in bulk economically with traditional, drop-casting
methods. Its cost should be comparable to that of conventional steels, Lu
said.
The researchers presented their findings in the June 18 issue of the journal
Physical Review Letters.
"In a nutshell, the key technological impact is that the invention of
amorphous steels can potentially revolutionize the steel industry," said
Joseph Poon, a materials physicist at the University of Virginia in
Charlottesville, who was not involved in the research.
Poon's team last April reported similar results in making amorphous steel in
bulk in the MRS Bulletin, the journal of the Materials Research Society.
The key was adding just a dash of yttrium. The rare-earth metal helps
frustrate the onset of crystallization even as the liquid steel approaches
its solidification temperature -- about 2,500 degrees Fahrenheit (1,370
degrees Celsius). The steel then can be shaped with conventional melting and
casting techniques. Poon noted the steels could even be processed like
plastic.
"When you produce a block of some metal and want to shape it, you can do
machining," Poon told UPI. "However, if you can treat these guys as
plastics, you can build a mold, and then when you cast it, you can just cast
it in. You can squeeze it, compress it, deform it, flatten it out, shape it
like plastics."
The centimeter-sized samples the researchers made showed extraordinary
strength and hardness, as well as no magnetism.
"The Navy wants to make non-magnetic submarine hulls," Poon said. "Right
now, the steels the Navy uses for submarine hulls are ferro-magnetic. You
don't want to be sitting in a mine field if you're sitting in a magnetic
field to begin with."
Among applications Lu listed for amorphous steel, in addition to buildings
and machinery, are armor-piercing projectiles, as well as electronics and
recreational equipment, such as fishing poles, tennis rackets, golf clubs
and bicycles. The publicly traded company Liquidmetal Technologies in Lake
Forest, Calif., owns an exclusive license to inventions made from amorphous
steels. The firm's customers include Samsung and Rawlings Sporting Goods Co.
"You could use some parts in motor vehicles," Poon said. "They're so strong,
you can reduce the quantity of steel you use (to) make (products) lighter."
Lu said further improvements will be necessary in the new steels to meet
scale-up challenges.
"The present amorphous steels, although strong, are still brittle. Thus,
more effort will be needed to improve on the ductility and damage
tolerance," Poon said. "Once the damage tolerance can be improved,
applications will soon be realistic."
There are several ways to improve these properties, Poon said. Ironically,
one is partial crystallization.
"Basically what you end up having is a composite of amorphous steel with
microcrystals or nanocrystals," he suggested.