Niche Applications for ORNL's Nickel Aluminides
Although ORNL-developed nickel aluminides are replacing steel components in niche applications, in one case they will likely help the steel industry.
Bethlehem Steel Corporation in Burns Harbor, Indiana, heat-treats steel plates so they can be shaped into components for bridges and other structures. Gear-driven steel rolls carry the plates into the furnace. But the rolls must be ground manually every two weeks before being put back into service.
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Conventional steel rolls at Bethlehem Steel (left and right) form
blisters that cause undesirable surface blemishes in steel plates,
the product of the steel mill. Rolls made of ORNL-developed nickel
aluminide (center, with arrows) show no signs of blistering. (Image
enhanced by Jamie Payne.) |
Otherwise, the steel plates
will be damaged because the intense heat eventually causes the steel rolls
to deform (so as to form blisters with sharp edges), sag, wobble, and
develop surface oxide particles. As a result, the plates can be beaten
up and scratched. Evidence indicates that use of nickel aluminide rolls
will not cause the concerns that the current steel rolls do.
Bethlehem Steel has replaced 20
of its 101 rolls with rolls made of ORNL’s nickel aluminide. Although
these 20 rolls have eliminated all of the issues raised by the currently
used rolls, the furnace must be shut down every other week because of
blister formation on the 81 steel rolls. Thus, the full benefit of using
ORNL-developed nickel aluminide in a steel mill won’t be known until all
101 rolls are made of this material, says Vinod Sikka, leader of the Materials
Processing Group in ORNL’s Metals and Ceramics Division (M&C). Fortunately,
the Department of Energy has approved $2.4 million to replace all 101
steel rolls with the new rolls made of nickel aluminide.
Delphi Automotive Systems in Saginaw, Michigan, is a major user of “furnace furniture” made of the ORNL-developed nickel aluminide, because the alloy is barely affected by the rapid heating-and-cooling cycles and embrittling effects of the furnace’s carbon atmosphere. The ORNL alloy is being used by Delphi in 500 trays for heating and hardening the surfaces of automobile parts (e.g., valves, ball bearings, and gears), replacing the conventionally used chromium-nickel alloyed steel (HU steel), which cannot endure these effects much longer than six months before falling apart. Research suggests that in furnace trays nickel aluminide has two to three times the life of HU steel.
Improved nickel aluminides were
developed in 1982 under the leadership of M&C’s Chain T. Liu, a corporate
fellow. ORNL researchers found the secret recipe for making nickel aluminide
highly ductile at room temperature so it could be shaped into useful components.
The trick is to add the right amounts of boron, chromium, molybdenum,
and zirconium. The resulting alloy also gets stronger at higher temperatures.
After 20 years, ORNL’s nickel aluminides are proving their value in niche
applications.
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