Pack Aluminization Synthesis of Superalloy 3D Woven and 3D Braided Structures
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PERIODIC cellular metals share desirable properties with stochastic metal foams such as low density, and high specific strength, stiffness, sound absorption, damping, and surface area.[1–9] Furthermore, periodic cellular metals can be micro-architectured to optimize various properties in an isotropic or anisotropic manner, which cannot be achieved with porous or foamed metals due to their irregular structures.[10,11] Some examples of periodic cellular materials are honeycombs,[2,3] trusses,[3–5] and assembly of helical wires,[6,7] which can all be used as the core of sandwich structures. Fabrication of such periodic structures from high-temperature alloys is highly desirable: for instance, cellular Ni-based superalloys could reduce the mass of jet engine parts while enabling efficient cooling which may enable increased operating temperature of the engine. Also, topologically tailored micro-architectures can be designed using optimization tools which offer, for example, optimized combination of high strength/stiffDINC ERDENIZ, Postdoctoral Fellow, and DAVID C. DUNAND, James N. and Margie M. Krebs Professor, are with the Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208. Contact e-mail: d-erdeniz@ northwestern.edu AMANDA J. LEVINSON, Postdoctoral Research Associate, is with the National Research Council Fellow US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375. KEITH W. SHARP, Product Manager, is with the 3D Fabrics, SAERTEX USA, LLC, 2200-A Mt. Holly-Huntersville Road, Huntersville, NC 28078. DAVID J. ROWENHORST, Materials Research Scientist, and RICHARD W. FONDA, Head, are with the Microstructural Evolution and Joining Section, US Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375. Manuscript submitted May 27, 2014. Article published online October 18, 2014 426—VOLUME 46A, JANUARY 2015
ness and high heat transfer properties for thermostructural applications.[12–14] However, there are severe limitations for the fabrication of such structures from high-strength superalloys with limited ductility, due to difficulties in cutting, shaping, and joining these high temperature alloys. A small number of studies report the production of periodic cellular superalloys,[15–17] none using property optimization tools. Nathal et al.[15] used investment casting to produce IN718 truss panels with 1.5 mm diameter struts and assembled them via hot isostatic pressing (HIP). Zhang and He[16] brazed honeycomb structures from corrugated 90 lm thick Ni-based alloy sheets. Murr et al.[17] created IN625 mesh structures with 0.6 to 1 pore per millimeter via additive manufacturing, using electron beam melting. To the best of our knowledge, there are no reports on the fabrication of woven or braided structures from superalloy wires, due to three significant manufacturing difficulties: (i) commercial superalloy wires are difficult to draw due to their limited ductility and are thus not widely available, especially below ~500 lm diameter; (ii)
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