σ and η Phase formation in advanced polycrystalline Ni-base superalloys

Stoichko Antonov*, Jiajie Huo, Qiang Feng, Dieter Isheim, David N. Seidman, Randolph C. Helmink, Eugene Sun, Sammy Tin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

In polycrystalline Ni-base superalloys, grain boundary precipitation of secondary phases can be significant due to the effects they pose on the mechanical properties. As new alloying concepts for polycrystalline Ni-base superalloys are being developed to extend their temperature capability, the effect of increasing levels of Nb alloying additions on long term phase stability and the formation of topologically close packed (TCP) phases needs to be studied. Elevated levels of Nb can result in increased matrix supersaturation and promote the precipitation of secondary phases. Long term thermal exposures on two experimental powder processed Ni-base superalloys containing various levels of Nb were completed to assess the stability and precipitation of TCP phases. It was found that additions of Nb promoted the precipitation of η-Ni6AlNb along the grain boundaries in powder processed, polycrystalline Ni-base superalloys, while reduced Nb levels favored the precipitation of blocky Cr and Mo – rich σ phase precipitates along the grain boundary. Evaluation of the thermodynamic stability of these two phases in both alloys using Thermo-calc showed that while σ phase predictions are fairly accurate, predictions of the η phase are limited.

Original languageEnglish (US)
Pages (from-to)232-240
Number of pages9
JournalMaterials Science and Engineering A
Volume687
DOIs
StatePublished - Feb 27 2017

Keywords

  • Ni6AlNb
  • Secondary phases
  • Sigma
  • Stability
  • Superalloy
  • Thermocalc

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Fingerprint Dive into the research topics of 'σ and η Phase formation in advanced polycrystalline Ni-base superalloys'. Together they form a unique fingerprint.

Cite this