Design of an Eta-Phase Precipitation-Hardenable Nickel-Based Alloy with the Potential for Improved Creep Strength Above 1023 K (750 °C)
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In a number of nickel-based superalloy systems strengthened by gamma prime (γ′), eta-phase (Ni3Ti, η) forms during prolonged high-temperature exposure, but its effect on mechanical properties is not well characterized. Using thermodynamic modeling and design-of-experiments techniques, three modifications of the nickel-based superalloy Nimonic (Nimonic® is a trademark of Special Metals Corporation group of companies.) 263 were identified that yield increased volume fractions of the eta-phase (Ni3Ti, η) at temperatures above 1023 K (750 °C). Volume fractions of η-phase were evaluated for each alloy and heat-treatment condition using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Compared to Nimonic 263, small additions of V and Ta were found to increase the volume fraction of η-phase above 1023 K (750 °C) from approximately 5 pct to above 15 pct, thus providing a route for future mechanical behavior experimental studies, which was not in the scope of this work.
KeywordsNi3Al Ni3Ti Increase Volume Fraction Large Volume Fraction Ni3Nb
Bruce Pint and Michael Santella of Oak Ridge National Laboratory are acknowledged for their support in melting the alloy compositions. The support of EPRI’s Technology Innovation Program on Advanced Materials, Program manager David Gandy, and initial research support from Peter Enz, Bryan Turner, and Ben Wittbrodt, is greatly acknowledged.
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