Characterization of the microstructure and phase equilibria calculations for the powder metallurgy superalloy IN100
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Gautam Ghosh and Gregory B. Olson Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208-3108
Martin J. Blackburn and Mark Aindow Department of Metallurgy and Materials Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (Received 28 March 2003; accepted 14 August 2003)
The microstructure of the Ni-based superalloy IN100 processed by a powder metallurgy route was evaluated to reveal the structures, volume fractions, distributions, and chemistries of the various phases present. These data were compared with those predicted by computational thermodynamics. It is shown that the microstructural parameters expected on the basis of global equilibrium conditions differ significantly from those measured experimentally. However, modification of these calculations by use of constrained and successive equilibria compensated for kinetic effects and led to accurate (or better) predictions of phase volume fractions and chemistries in this alloy. This demonstrated that such modified phase equilibria calculations could be powerful tools for modeling microstructures, even in complex multicomponent alloys processed under nonequilibrium conditions.
I. INTRODUCTION
Nickel-based superalloys are widely used in situations requiring superior strength at high temperatures and consequently find extensive application in the hot sections of gas turbine and rocket engines and nuclear reactors. A large number of publications have appeared over the 40-year history of these alloys including a regular series of conference proceedings1 that cover the structural, processing, and performance characteristics of these materials. The reader is referred to such articles for the general background of the project described here. This current work was performed on one of the oldest superalloys, IN100, developed in the early 1960s, but still used today in the cast or powder metallurgy (P/M) forms. Powder processing results in remarkable chemical and structural homogeneity and excellent strength and toughness properties, but poorer creep and rupture capability restricts application at the highest temperatures. Thus, the P/M form of IN100 is used mainly in jet engines for
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Address all correspondence to this author. Present address: Pratt & Whitney, 400 Main Street M/S 114-40, East Hartford, CT 06108. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 11, Nov 2003
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parts operating in the intermediate temperature regime, especially for components such as disks, spacers, and seals. The two major phases present in IN100 alloy are the ordered ␥⬘ (Ni3Al-type) phase together with a disordered solid-solution ␥ matrix; the relative volume fractions are approximately 60:40. Carbides and borides occur as minor phases. The strength of this class of superalloys depends on a number of interrelated microstructural parameters including the volume fraction, particle size, distribution, and chemical characteristics of
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