Lab's Laser Key to Strong Metals: Free-electron technique tested locally shows promise (Daily Press)
Lab's Laser Key to Strong Metals:
Free-electron technique tested locally shows promise
By Michael Hines, Daily Press
March 12, 2001
NEWPORT NEWS - In one thousandth of a second, Peter Schaaf can make silicon 10 times stronger — and that someday may help auto makers and other industries save millions of dollars.
Schaaf, an associate professor of physics and material science at the University of Gottingen, returned to Germany earlier this week after spending all of last week in Newport News experimenting with a new way of bonding metals with nitrogen atoms.
Industries, such as tool makers and car makers, use that process to make metals harder and more corrosion-resistant.
Schaaf said he improved his technique by using the free-electron laser at the Thomas Jefferson National Accelerator Facility.
Its ability to change how much power is in its laser meant he was able to find the level best suited for individual metals, a feat that conventional lasers can't accomplish. That also means less risk to the metal's helpful aspects, such as surface hardness and durability.
"This is a great advantage," he said. "When you have expensive parts, if you heat them too much, they may lose their beneficial properties."
The big selling point of the process, however, is that it improves those metals without the cost and time typically involved.
Schaaf has been a man of steel, titanium and silicon for the past six years. Four years ago, his research found a way to strengthen metals faster than a speeding bullet.
Most techniques use a vacuum chamber, a machine that sucks all the air from an area where a material needs nitriding. Nitriding is a process that forms a hard shell around metal by combining it with nitrogen.
The vacuum ensures that only nitrogen bonds with the metal, reducing the risk that cracks or other imperfections will form.
"It's like a ceramic layer, and ceramics are much more durable than metals," said Mool Gupta, Old Dominion University director of the Applied Research Center, who was not involved with the experiment. "You have a metal and form a ceramic coating around it. That gives you better protection."
The process can make titanium four times stronger, Schaaf said, while steel can get four to six times stronger.
But the vacuum costs at least $100,000 for commercial ventures, said Brian Holloway, assistant professor in the Department of Applied Science at the College of William and Mary.
Even after the hours it takes to empty the chamber, he said, the actual nitriding process can then take several days to complete.
"Vacuum systems are expensive, first of all," said Holloway, who was not involved with Schaaf's research. "They're time consuming, second of all."
By eliminating the vacuum chamber, Schaaf said, the process time is cut to a few hours.
At Jefferson Lab, his experiments used square inch samples of metals, including titanium, iron, steel and aluminum.
Instead of adding nitrogen into a vacuum chamber, Schaaf simply sprayed nitrogen across the material while shooting the metal with Jefferson Lab's laser.
The laser heats the gas and metal surface — sometimes to nearly as hot as the sun in one billionth of a second — and allows nitrogen crystals to form inside the metal surface, less than a hair's width deep.
Four years ago, Schaaf conducted a similar experiment in Germany without a vacuum chamber or a laser that could be adjusted.
Work with the free-electron laser could mean finding just the right set-up for industries to duplicate Schaaf's work without building a similar laser, Holloway said.
That, in turn, could mean a cheaper nitriding process as well as possibly material costs.
Industries using steel, for example, could work with more malleable metals and then strengthen them using the nitriding process, Holloway said.
Gupta said the technique shows promise.
"It's an interesting process," he said.