γ+γ′ microstructures in the Co-Ta-V and Co-Nb-V ternary systems

Fernando L. Reyes Tirado, Jacques Perrin Toinin, David C. Dunand*

*Corresponding author for this work

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

The Co-Ta-V and Co-Nb-V ternary systems are investigated in a search for L12-ordered γ′ precipitation, based on recent computational predictions of stable γ+γ′ microstructures. Four alloys with nominal (at. %) composition Co-6Ta-6V, Co-5.4Ta-6.6V-xNi (x = 0 and 10), and Co-6Nb-6V are arc-melted, homogenized at 1250 °C, and aged at 900 °C for 2, 16 and 64 h. Nanometric, cuboidal γ′ precipitates within a fcc-γ matrix are discovered in the Co-Ta-V system after aging for 2 h, and in the Co-Nb-V system after cooling from homogenization. The compositions of these two new γ′-phases, as measured via atom probe tomography, are Co3(Ta0.76V0.24) and Co3(Nb0.65V0.35), respectively. Upon aging at 900 °C, the γ′ precipitates coarsen, dissolve and transform to lamellar C36-Co3(Ta,V) and needle-shape D019-Co3(Nb,V), measured as Co3(Nb0.81V0.19) by APT, respectively. This shows that these ternary γ′ phases are metastable and points to the need for their stabilization via additional alloying elements.

Original languageEnglish (US)
Pages (from-to)137-148
Number of pages12
JournalActa Materialia
Volume151
DOIs
StatePublished - Jun 1 2018

Keywords

  • Atom probe tomography (APT)
  • Cobalt-base superalloys
  • Intermetallic phases
  • Microstructure
  • Precipitates

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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