MC Carbide Characterization in High Refractory Content Powder-Processed Ni-Based Superalloys
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ODUCTION
NICKEL-BASED superalloys are used as the materials for high-temperature components in modern gas turbine engines due to their high strength along with considerable creep and fatigue resistance even when exposed to corrosive environments, high stress levels, and elevated temperatures.[1–9] The superior high-temperature properties of Ni-based superalloys can largely be attributed to the unique microstructure consisting of STOICHKO ANTONOV is with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China and also with the Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616. Contact e-mail: [email protected] WEI CHEN and SAMMY TIN are with the Illinois Institute of Technology. JIAJIE HUO and QIANG FENG are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing. DIETER ISHEIM and DAVID N. SEIDMAN are with the Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 and also with the Northwestern University Center for Atom Probe Tomography (NUCAPT), 2220 Campus Drive, Evanston, IL 60208. EUGENE SUN is with the Rolls-Royce Corporation, PO Box 420, Indianapolis, IN 46241. Manuscript submitted January 18, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
ordered L12 intermetallic precipitates, c¢ (Ni3Al), distributed coherently within a disordered FCC A1 matrix, c (Ni), that provide substantial order and coherency type strengthening by inhibiting dislocation motion during plastic deformation. The composition of Ni-based superalloys tends to incorporate a variety of elemental additions, each focused at improving a certain property. For example, refractory alloying elements, such as W, Mo, Cr and Co, in modern polycrystalline Ni-based superalloys serve to strengthen the c matrix phase through solid solution strengthening, while concentrations of c¢-forming Al, Ti, Nb, and Ta are utilized to produce an optimized volume fraction of the c¢ strengthening phase as they will preferentially partition to the c¢ phase. The c¢-forming elements also serve to lower the antiphase boundary energy as well as to strengthen the precipitate’s resistance to dislocation shear.[10] Moreover, elevated concentrations of these elements may induce partitioning to the c phase that can act as potent solid solution strengthener.[11–14] In addition, certain refractory elements can bond with various trace elements, such as C, N, and O, to produce carbides, nitrides and oxides, which could be either detrimental or beneficial to the mechanical properties depending on the type of compound that forms.[15]
Carbides in Ni-based superalloys are typically desired microstructural features as they can contribute to the strengthening of the c matrix by inhibiting dislocation motion, when present intragranularly, as well as pin grain boundaries and help in structural refinement during fabrication and processing of the material, when dispersed through the grai
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