An investigation of diffusion-mediated cyclic coarsening and reversal coarsening in an advanced Ni-based superalloy

Yiqiang Chen, R. Prasath babu, Thomas J.A. Slater, M. Bai, Robert Mitchell, Octav Ciuca, Michael Preuss, Sarah J. Haigh

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Abstract

The anomalous cyclic coarsening behaviour of γ′ precipitates after ageing at 1073 K has been investigated for the low misfit commercial powder metallurgy (PM) Ni-based superalloy RR1000. Using scanning transmission electron microscope (STEM) imaging combined with absorption-corrected energy-dispersive X-ray (EDX) spectroscopy, the elemental segregation as a function of coarsening behaviour has been experimentally observed for secondary γ′ precipitates. Elemental EDX spectrum imaging has revealed nanoscale enrichment of Co and Cr and a depletion of Al and Ti within the γ matrix close to the γ-γʹ interface. Our experimental results, coupled with complementary modelling and synchrotron X-ray diffraction analysis, demonstrate the importance of elastic strain energy resulting from local compositional variations for influencing precipitate morphology. In particular, elemental inhomogeneities, as a result of complex diffusive interactions within both matrix and precipitates, play a crucial role in determining the rate of coarsening. Our findings provide important new evidence for understanding the microstructural evolution observed for advanced superalloys when they are exposed to different heat treatment regimes.
Original languageEnglish
Pages (from-to)295-305
Number of pages11
JournalActa Materialia
Volume110
Early online date24 Mar 2016
DOIs
Publication statusPublished - 15 May 2016
Externally publishedYes

Bibliographical note

© 2016 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Keywords

  • Ni based superalloys
  • coarsening
  • precipitates
  • Scanning transmission electron microscopy
  • elemental mapping
  • energy dispersive X-ray spectroscopy

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