Source:High Technology Business 9.n9 (Nov-Dec 1989): pp12(2). (640
words)
High-Voltage Metallurgy
STEEL IS never strong enough. Copper and aluminum are not ductile
enough, and tungsten is too brittle. But by exposing these useful
metals to strong voltages, their properties can be modified and their
usefulness enhanced. This new metallurgy is being advanced by a
research team at North Carolina State University, Raleigh, led by Hans
Conrad, professor of metallurgy.
The electrostatic effect is one of several metal modifiers under
study. Conrad is also experimenting with the effects of high currents
and magnetic fields on the processibility of metals.
The team's work began 10 years ago when it received funding the
investigate the effects of current pulses of 1 million to 10 million
amperes on metals. Because the currents are applied for only 50-to 100
microseconds, they do not vaporize the metal samples. But they make
metals, particularly fragile tungsten, much easier to process. This
early work was based on prior research by Russian metallurgists, who
began investigating the effects of current pulses on metals more than
20 years ago.
After confirming the Russian work, Conrad's team turned to high-
voltage effects about 18 months ago. They exposed various metals,
including lead and nickel, to electrostatic forces of from 1- to 10-
kilovolts per centimeter. Result: Steel subjected to the electrical
field during heat treatment comes out twice as hard; the temperature
at which copper begins to soften doubles from 200 degrees Fahrenheit
to 400 degrees Fahrenheit; and an aluminum alloy can be stretched like
chewing gum without developing Swiss-cheeselike holes. However,
attempts to create tough composites of steel reinforced with high-
melting-point tungsten fibers have been hobbled by the fibers'
tendency to crumble.
Enhancing aluminum is particularly significant, because the team's
work is financed in part by the Aluminum Company of America, the
Pittsburgh-based aluminum-manufacturing giant. Conrad claimed that
Alcoa's experts are very excited about the research results. Most of
the team's funding--about $1 million--comes from the U.S. Army
Research Office in nearby Research Triangle Park, N.C.
The military's interest is understandable: Highly ductile, or
"superplastic," metals could have applications in the manufacture of
advanced aircraft; and increasing the ductibility of tungsten could
result in much-tougher armor for tanks and other military vehicles.
Furthermore, the Army wants to find out what electrostatic forces do
to the barrel of a cannon, because in the future, shells may be
propelled out of cannons by powerful electrostatic forces instead of
gunpowder. Easily malleable tungsten fibers would also be of interest
to manufacturers of incandescent light bulbs.
Although the investigation is still in its preliminary stages, NCSU
has made patent disclosures to the U.S. Patent and Trademark Office
and hopes to file for patents worldwide. One promising area for
investigation is combining electrostatically generated effects with
other effects, such as magnetism. The team uses a liquid helium bath
to support a powerful magnet made of superconducting materials. Conrad
cited the work of Robert Hoffmann, a researcher at the Georgia
Institute of Technology, Atlanta, who reportedly tripled the life of
tool bits by treating them with strong magnetic forces. Conrad's team
also applied electrostatic forces to niobium in its superconducting
state producing "interesting" but incomplete results.
The electrostatic effect has so far been applied to small samples,
none more than an eighth of an inch thick. To treat thicker samples,
more-powerful voltage sources are needed. The effect is regressively
logarithmic--when voltage is doubled, the result is less than double.
This suggests that an upper-voltage limit of diminishing returns would
soon be reached. On the other hand, Conrad said that no threshold
voltage has been detected. In other words, lesser effects can be
achieved with low voltages.
Treating metals with various forces is so intriguing to Conrad that he
organized a conference on the subject that took place last July in
Raleigh. Besides electrostatic, high-current, and magnetic effects,
the conference considered the effects of lasers and ultrasonic energy.
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