Eutectic Superalloys 690689

Unidirectionally solidified eutectics offer a favorable approach for producing high strength multiphase materials where one phase serves as the matrix and the other phase or phases serve as the reinforcement. In addition to high strengths, these composite materials generally exhibit excellent microstructural stability at elevated temperature.
As a representative of the class of materials that shall be referred to as eutectic superalloys, the mechanical characteristics of the Ni3Al-Ni3Cb eutectic are discussed and compared with commercially available superalloys. The thermal expansion and oxidation behavior of this alloy are also discussed. The microstructure of this material is lamellar in nature and consists of approximately 44 vol % of the reinforcing phase Ni3Cb in a matrix of Ni3Al. Its melting temperature is 1280 C (2335 F), the eutectic composition is 68 wt % Ni3Cb, and its density is approximately 8.5 gm/cc (0.3 lb/cu in.).
The mechanical properties discussed include tensile, creep-rupture and impact. The tensile strength of this eutectic at 2000 F, parallel to the direction of phase alignment, is approximately 100,000 psi. Creep-rupture specimens tested in air at 2000 F exhibited a 100 hr rupture strength of approximately 25, 000 psi. Although this alloy contains 44% of a brittle phase it still possesses useful impact toughness. The hot strength of this eutectic superalloy, which is markedly superior to currently available nickel-base supperalloys, indicates that it may be important as a turbine component in advanced gas turbine engines.


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