Environmentally-assisted grain boundary attack as a mechanism of embrittlement in a nickel-based superalloy

Research output: Contribution to journalArticlepeer-review

Authors

  • A. A.N. Németh
  • D. J. Crudden
  • D. E.J. Armstrong
  • K. Li
  • A. J. Wilkinson
  • C. R.M. Grovenor
  • R. C. Reed

Colleges, School and Institutes

External organisations

  • OXFORD UNIVERSITY

Abstract

The loss of ductility in the high strength polycrystalline superalloy 720Li is studied in air between room temperature and 1000 °C. Tensile ductility is influenced profoundly by the environment, leading to a pronounced minimum at 750 °C. A relationship between tensile ductility and oxidation kinetics is identified. The physical factors responsible for the ductility dip are established using energy-dispersive X-ray spectroscopy, nanoscale secondary ion mass spectrometry and the analysis of electron backscatter diffraction patterns. Embrittlement results from internal intergranular oxidation along the γ-grain boundaries, and in particular, at incoherent interfaces of the primary γ precipitates with the matrix phase. These fail under local microstresses arising from the accumulation of dislocations during slip-assisted grain boundary sliding. Above 850 °C, ductility is restored because the accumulation of dislocations at grain boundaries is no longer prevalent.

Details

Original languageEnglish
Pages (from-to)361-371
Number of pages11
JournalActa Materialia
Volume126
Publication statusPublished - 1 Mar 2017

Keywords

  • Ductility minima, Environmentally-assisted cracking, Ni-based superalloy, Oxidation