High resolution energy dispersive spectroscopy mapping of planar defects in L12-containing Co-base superalloys

Michael S. Titus, Alessandro Mottura, G. Babu Viswanathan, Akane Suzuki, Michael J. Mills, Tresa M. Pollock

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Abstract

Local chemical fluctuations in the vicinity of superlattice intrinsic stacking faults (SISFs) have been observed via high resolution energy dispersive X-ray spectroscopy (EDS) mapping in new single crystal Co- and CoNi-base superalloys containing γ′-(L12) precipitates. The SISFs were formed during high temperature tensile creep at 900 °C. Chemical fluctuations were found to greatly influence the SISF energy, which was calculated from density functional theory in Co3(Al, Ta, W) compounds at 0 K. The local SISF structure was found to be comprised of four D019 (0001) planes that were enriched in W and Ta, as revealed by high resolution scanning transmission electron microscopy (HRSTEM) imaging and EDS mapping. The precipitates were determined to accommodate up to 22% of the plastic deformation accrued during an interrupted creep test to 0.6% creep strain. The driving forces for segregation are discussed, and new models for shearing of the ordered precipitates are proposed.
Original languageEnglish
Pages (from-to)423–437
JournalActa Materialia
Volume89
Early online date4 Mar 2015
DOIs
Publication statusPublished - 1 May 2015

Keywords

  • Cobalt alloys
  • High temperature creep
  • Scanning transmission electron microscopy
  • Energy dispersive X-ray spectroscopy
  • Stacking faults

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