Successful development of advanced gas turbine engines for aircraft will require lightweight, high-temperature components. Currently titanium-aluminum- (TiAl) based alloys are envisioned for such applications because of their lower density (~4 g/cm3) in comparison to superalloys (~8.5 g/cm3), which have been utilized for hot turbine engine parts for over 50 years. However, a recently developed concept (lattice block) by JAMCORP, Inc., of Willmington, Massachusetts, would allow lightweight, high-temperature structures to be directly fabricated from superalloys and, thus, take advantage of their well-known, characterized properties.
IN 718 superalloy open cell lattice block panel formed by small-diameter, straight ligaments in a triangulated trusslike geometry. Top: Overview. Bottom: Magnified view.
In its simplest state, lattice block is composed of thin ligaments arranged in a three-dimensional triangulated trusslike configuration that forms a structurally rigid panel as illustrated in the figure. This panel, which was produced by investment casting, contains about 2250 ligaments, 1.6 mm in diameter, which form a 130- by 290- by 11-mm-thick netlike structure that weighs 85-percent less than a similar size solid plate. Because lattice block can be fabricated by casting, correctly sized hardware is produced with little or no machining; thus very low cost manufacturing is possible.
Together, the NASA Glenn Research Center and JAMCORP have extended their lattice block methodology for lower melting materials, such as Al alloys, to demonstrate that investment casting of superalloy lattice block is possible. This effort required advances in lattice block pattern design and assembly, higher temperature mold materials and mold fabrication technology, and foundry practice suitable for superalloys (ref. 1). Lattice block panels have been cast from two different Ni-base superalloys: IN 718, which is the most commonly utilized superalloy and retains its strength up to 650 °C; and MAR M247, which possesses excellent mechanical properties to at least 1100 °C. In addition to the open-cell lattice block geometry illustrated in the figure, same-sized lattice block panels containing a thin (~1-mm-thick) solid face on one side have also been cast from both superalloys.
Initial tensile, compression, bend, and fatigue tests of samples machined from IN 718 open-cell lattice block (see the figure) have been completed and are described in reference 2. This work indicated that the trusslike structure can redistribute the applied load, which provides the redundancy leading to graceful failure. The test data, when combined with finite element analysis of the ligament structure, indicate that the ligaments could support stresses consistent with the strength of IN 718.
The elevated-temperature mechanical properties of the open cell and face-sheeted superalloy lattice block panels are currently being examined, and the microstructure is being characterized in terms of casting defects. In addition, a small study (ref. 3) is being undertaken with GE Aircraft Engines to determine the suitability of superalloy lattice block for engine components.
Glenn contact: Dr. J.Daniel Whittenberger, 216-433-3196, John.D.Whittenberger@nasa.gov
Authors: Dr. Mohan G. Hebsur, Dr. J, Daniel Whittenberger, and David L. Krause
Headquarters program office: OAT
Programs/Projects: UEET
Last updated: June 25, 2003
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