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On the effect of Re addition on microstructural evolution of a CoNi-based superalloy

Pandey, P and Sawant, AK and Nithin, B and Peng, Z and Makineni, SK and Gault, B and Chattopadhyay, K (2019) On the effect of Re addition on microstructural evolution of a CoNi-based superalloy. In: ACTA MATERIALIA, 168 . pp. 37-51.

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Official URL: https://dx.doi.org/10.1016/j.actamat.2019.01.046

Abstract

In this study, the effect of rhenium (Re) addition on microstructural evolution of a new low-density Co-Ni-Al-Mo-Nb based superalloy is presented. Addition of Re significantly influences the gamma' precipitate morphology, the gamma/gamma' lattice misfit and the gamma/gamma' microstructural stability during long term aging. An addition of 2 at.% Re to a Co-30Ni-10Al-5Mo-2Nb (all in at.%) alloy, aged at 900 degrees C for 50 h, reduces the gamma/gamma' lattice misfit by similar to 40% (from +0.32% to +0.19%, measured at room temperature) and hence alters the gamma' morphology from cuboidal to round-cornered cuboidal precipitates. The composition profiles across the gamma/gamma' interface by atom probe tomography (APT) reveal Re partitions to the gamma phase (K-Re = 0.34) and also results in the partitioning reversal of Mo to the gamma phase (K-Mo = 0.90) from the gamma' precipitate. An inhomogeneous distribution of Gibbsian interfacial excess for the solute Re (Gamma(Re), ranging from 0.8 to 9.6 atom.nm(-2)) has been observed at the gamma/gamma' interface. A coarsening study at 900 degrees C (up to 1000 h) suggests that the coarsening of gamma' precipitates occurs solely by evaporation-condensation (EC) mechanism. This is contrary to that observed in the Co-30Ni-10Al-5Mo-2Nb alloy as well as in some of the Ni-Al based and high mass density Co-Al-W based superalloys, where gamma' precipitates coarsen by coagulation/coalescence mechanism with an extensive alignment of gamma' along <100> directions as a sign of microstructural instability. The gamma' coarsening rate constant (K-r) and gamma/gamma' interfacial energy are estimated to be 1.13 x 10(-27) m(3)/s and 8.4 mJ/m(2), which are comparable and lower than Co-Al-W based superalloys.

Item Type: Journal Article
Additional Information: The copyright for this article belongs to Elsevier
Keywords: Rhenium (Re); Cobalt-based superalloys; Lattice misfit; Atom probe tomography (APT); Coarsening kinetics
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Depositing User: Ms Ranganayaki RS
Date Deposited: 30 Apr 2019 04:37
Last Modified: 30 Apr 2019 04:37
URI: http://eprints.iisc.ac.in/id/eprint/62536

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