Oak Ridge National Laboratory

 

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Exo-Melt process could put amiable alloy in auto, steel plants

OAK RIDGE, Tenn., Sep. 15, 1995 — To the automotive and steel industries, nickel aluminide is an attractive alloy, but it has a major drawback: it is difficult to produce.

The alloy, invented at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) in the mid-1980s, is made by melting nickel and aluminum together in a specific proportion. It is corrosion resistant, remains strong at high temperatures and it contains no expensive or rare materials. These characteristics make the alloy ideal for placement in furnaces used in the automobile industry to produce various parts, including valves, ball joints and gears. Unfortunately, people in the alloy production industry had some safety concerns and many simply would not produce nickel aluminide.

Researchers at ORNL, however, have now addressed that problem with the Exo-Melt ' process, which eased one of the major obstacles to producing nickel aluminide.

"Vendors had experience adding very small amounts of aluminum to steel, but they resisted melting material that contained as much as 12 percent aluminum (as nickel aluminide contains)," said ORNL's Vinod Sikka, who worked with colleagues Joseph Vought and Seetharama Deevi to develop the process. Deevi is on sabbatical at ORNL from Philip Morris Co. "The vendors feared that the molten aluminum would leak through tiny cracks in the furnace wall and attack the heating coils, possibly causing an explosion."

The Exo-Melt process, which received a 1995 R&D 100 Award from R&D Magazine, is a new method of loading the furnace to take advantage of the heat generated in the reaction between nickel and aluminum, Sikka said.

"The reaction that produces the nickel aluminide frees a large amount of heat and is, therefore, called an exothermic reaction," Sikka said. This heat increases the efficiency of the process that creates nickel aluminide by dissolving the alloying metals to produce additional nickel aluminide.

The Exo-Melt process leads to parts that cost less to produce because it uses as much as 50 percent less electricity than is required by other alloy-manufacturing processes. Nickel aluminide parts are also more durable than other alloys, as an experiment at a General Motors plant in Saginaw, Mich., proved. In the experiment, two trays - one made of the conventional iron-chrome-nickel alloy (HU steel), the other made of nickel aluminide - were subjected to cycles of heating and rapid cooling. After six months of this treatment, the conventional steel trays fell apart while the nickel aluminide trays showed no effects of the heat.

"General Motors concluded that nickel aluminide has at least twice the life of the HU steel that they have been using in their furnace trays," Sikka said. "Continued tests may show that nickel aluminide lasts three to five times longer than conventional steel."

Other companies, including a major U.S. steel company, report similar findings. Rollers used to move steel plates during the heat treating process typically lose strength, sag and wobble, all of which cause problems as the heated steel plates travel across the rollers on their way through the production cycle. The rollers also develop needle-like oxides that scratch the steel plates.

"That's a problem because their competitors in Japan are selling steel plates that are not scratched," Sikka said.

The steel company's engineers believe rollers made of nickel aluminide will be three times stronger than steel ones. Instead of shutting down operations every three weeks to replace deteriorated rollers, as they do now, the company's engineers expect shutdowns to be necessary just once a year, resulting in vastly improved productivity. Furthermore, while the current process of manufacturing results in 40 percent of the steel plates being scratched, the new rollers will result in scratch-free steel.

Other uses for nickel and iron aluminides, which can also be manufactured using the Exo-Melt process, include manufacturing tooling such as dies, pumps and water turbines, heating elements for stoves, ovens and dryers and hot gas filters used for coal gasification.

ORNL, one of DOE's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Systems, which also manages the Oak Ridge K-25 Site and the Oak Ridge Y-12 Plant. Funding for the research was provided by the DOE Energy Efficiency's Advanced Industrial Materials Program, Fossil Energy's Advanced Research and Technology Development Materials Program, and Energy Research's Basic Energy Sciences Materials Program.

You can learn more about this research and many other exciting projects by visiting ORNL Oct. 21, 1995, during its Community Day. Many of the lab's facilities will be open to the public that day. For additional information, call ORNL Public Affairs, 865-574-4160.