Comparison of Thermodynamic Predictions and Experimental Observations on B Additions in Powder-Processed Ni-Based Supera
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Comparison of Thermodynamic Predictions and Experimental Observations on B Additions in Powder-Processed Ni-Based Superalloys Containing Elevated Concentrations of Nb STOICHKO ANTONOV , JIAJIE HUO, QIANG FENG, DIETER ISHEIM, DAVID N. SEIDMAN, EUGENE SUN, and SAMMY TIN Boron additions to Ni-based superalloys are considered to be beneficial to the creep properties of the alloy, as boron has often been reported to increase grain boundary cohesion, increase ductility, and promote the formation of stable boride phases. Despite the importance, it is not well understood whether these improvements are associated with the presence of elemental boron or stable borides along the grain boundaries. In this investigation, two experimental powder-processed Ni-based superalloys containing elevated levels of Nb were found to exhibit increased solubility for B in the c matrix when compared to similar commercial Ni-based superalloys. This resulted in an overall lower B concentration at grain boundaries that suppressed boride formation. As the predictive capability of CALPHAD database models for Ni-based superalloys have improved over the years, some discrepancies may still persist around compositionally heterogeneous features such as grain boundaries. Improved quantification of the characteristic partitioning of B as a function of the bulk alloy composition is required for understanding and predicting the stability of borides. DOI: 10.1007/s11661-017-4380-7 The Minerals, Metals & Materials Society and ASM International 2017
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INTRODUCTION
EXCELLENT mechanical properties, such as high temperature creep and fatigue resistance, along with high corrosion and oxidation resistance, while operating at high stress levels and elevated temperatures are the properties that make nickel-based superalloys the material used for the ‘‘hot section’’ components in modern gas turbine engines.[1–9] These superior high temperature properties can largely be attributed to the unique microstructure of Ni-based superalloys, which consists of ordered L12 intermetallic precipitates c¢ (Ni3Al) distributed coherently within a disordered FCC A1 STOICHKO ANTONOV and SAMMY TIN are with the Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616. Contact e-mail: [email protected] JIAJIE HUO and QIANG FENG are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China. 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 June 30, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
matrix c (Ni) that provides substantial order and coherency type strengthening by inhibiting dislocation motion during plastic deformation. The composition of modern
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