Segregation and η phase formation along stacking faults during creep at intermediate temperatures in a Ni-based superalloy

T. M. Smith, B. D. Esser, N. Antolin, G. B. Viswanathan, T. Hanlon, A. Wessman, D. Mourer, W. Windl, D. W. McComb, M. J. Mills

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Abstract

In this paper, the local compositional and structural changes occurring in association with stacking faults in a Ni-base superalloy are characterized and related to the possible rate-controlling processes during creep deformation at intermediate temperatures. These rate-controlling processes are not presently understood. In order to promote stacking fault shearing, compression creep tests on specially prepared single crystals of an exploratory Ni-base superalloy were conducted at 760 °C in the [0 0 1] orientation. Scanning transmission electron microscopy (STEM) imaging was coupled with state-of-the-art energy dispersive X-ray (EDX) spectroscopy to reveal for the first time an ordered compositional variation along the extrinsic faults inside the γ′ precipitates, and a distinct solute atmosphere surrounding the leading partial dislocations. The local structure and chemistry at the extrinsic fault is consistent with the η phase, a D024 hexagonal structure. Density Functional Theory (DFT) and high angle annular dark field (HAADF)-STEM image simulations are consistent with local η phase formation and indicate that a displacive-diffusive transformation occurs dynamically during deformation.

Original languageEnglish
Pages (from-to)19-31
Number of pages13
JournalActa Materialia
Volume100
DOIs
Publication statusPublished - Nov 2015
Externally publishedYes

Keywords

  • Atomic resolution EDS
  • DFT
  • EDX
  • HAADF
  • HAADF simulation
  • Ni-based superalloy
  • Phase transformation
  • Segregation
  • SESF
  • Single crystal creep
  • STEM
  • η phase

Cite this

Smith, T. M., Esser, B. D., Antolin, N., Viswanathan, G. B., Hanlon, T., Wessman, A., Mourer, D., Windl, W., McComb, D. W., & Mills, M. J. (2015). Segregation and η phase formation along stacking faults during creep at intermediate temperatures in a Ni-based superalloy. Acta Materialia, 100, 19-31. https://doi.org/10.1016/j.actamat.2015.08.053