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New composite has promise for wear parts, engine components

OAK RIDGE, Tenn., Nov. 28, 1995 — A new group of composites developed by a researcher at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) has many attributes that could be valuable to industries, according to their developer, Joachim Schneibel.

Schneibel, a physicist in ORNL's Metals and Ceramics Division, believes his composites will be useful in wear applications, such as engine or pump components. In particular, these composites might be suitable for wear applications in oxidizing or sulfidizing environments, Schneibel said.

Schneibel fabricates his composites by liquid phase sintering of ceramic powders with an iron aluminide binder. The binder has a typical composition of iron aluminide (Fe-24 wt% Al) and offers high resistance to corrosion, oxidation and sulfidation.

Depending on the intended uses, ceramic powders such as tungsten carbide, titanium carbide, titanium diboride or zirconium diboride may be used. The composites contain 40 percent to 70 percent ceramics and exhibit a high strength-to-weight ratio. They can be processed by conventional powder metallurgical techniques. Another advantage of the composites is that they contain no nickel or cobalt, which can cause problems to the environment and to workers because dust from nickel and cobalt is toxic.

Other advantages of the iron aluminide/ceramic composite include: - significantly lower cost of the iron aluminide binder as compared to cobalt; - densities as low as 5-6 grams per cubic centimeter; - hardnesses approaching those of tungsten carbide; - fracture toughness between 15-30 megapascals x meter1/2 (MPa x m1/2); - bend strengths approaching 1,500 MPa; - dry wear characteristics superior to silicon nitride; and - torch brazing capability.

Furthermore, the iron aluminide binder is non-magnetic, so it will not interact with magnetic powders and materials. The composites can be machined using electro discharge, a method of machining that is often faster, more precise and less expensive than other methods.

This research was sponsored by DOE's Office of Basic Energy Sciences, Division of Materials Sciences.

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.