Suzuki segregation in Co-Ni-based superalloy at 973 K: An experimental and computational study by phase-field simulation

Yuichiro Koizumi, Takeshi Nukaya, Sho Suzuki, Shingo Kurosu, Yunping Li, Hiroaki Matsumoto, Kazuhisa Sato, Yuji Tanaka, Akihiko Chiba

Research output: Contribution to journalArticlepeer-review

47 Citations (Scopus)

Abstract

Suzuki segregation in Co-Ni-based superalloys is of longstanding interest. In this study, the development of widely extended stacking fault (SF) ribbons was confirmed in a Co-Ni-based superalloy aged at 973 K after deformation at room temperature, which supports the decrease in stacking fault energy (SFE) due to Suzuki segregation. In addition, the plastic deformation behaviors of Co-Ni-based superalloys with various Nb contents up to 3 wt.% were investigated focusing on the effect of Nb addition on dynamic strain-aging by Suzuki segregation. The negative strain-rate dependence of flow stress due to dynamic strain-aging became more significant with increasing Nb content; however, attempts to detect segregating elements by scanning transmission electron microscopy and energy-dispersive spectroscopy analysis were not successful. A phase-field simulation of Suzuki segregation suggested strong Ni depletion with segregation of Cr and Mo atoms at the SF, and the SFE can become negative as a consequence of the segregation. This agrees with the experimentally observed formation of wide SFs by the aging at 973 K after cold deformation. It is also suggested that Nb atoms are strongly depleted at SFs, and a small amount of Nb addition dramatically enhances Cr segregation, resulting in further decreases in the SFE, which is probably responsible for the observed enhancement of dynamic strain-aging by Nb addition. In addition, the local structural changes, such as short-range ordering and/or an in-plane ordering, accompanying the segregation were discussed as possible additional mechanisms for strain-aging enhancement.

Original languageEnglish
Pages (from-to)2901-2915
Number of pages15
JournalActa Materialia
Volume60
Issue number6-7
DOIs
Publication statusPublished - 2012 Apr
Externally publishedYes

Keywords

  • Interface segregation
  • Phase field models
  • Refractory metals
  • Strain-aging
  • Transmission electron microscopy (TEM)

ASJC Scopus subject areas

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

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