A transmission electron microscopy study of EBR-II neutron-irradiated austenitic stainless steel 304 and nickel-base alloy X-750

Xiang Liu, Lingfeng He, Huan Yan, Mukesh Bachhav, James F. Stubbins

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Abstract

The microstructure of EBR-II neutron-irradiated austenitic stainless steel 304 and nickel-base alloy X-750 was investigated. Both alloys were irradiated at low dose rates (∼2 × 10−8 dpa/s) to a neutron fluence of 6.9 × 1022 n/cm2 (E > 0.1 MeV) at 371–389 °C. Different types of defects, including Frank loops, cavities, and precipitates were characterized. The Frank loops in Type 304 stainless steel (SS) are larger in size (∼50 nm in diameter) and lower in number density (2.58 × 1021 m−3), compared to most previous higher dose rate neutron irradiation studies. The Frank loops in X-750 have an average size 26.0 nm of and a number density of 9.44 × 1021 m−3. In 304 SS and X-750, cavities are of ∼20 nm and ∼14 nm in diameter, respectively. The swelling of both alloys was found to be insignificant. In 304 SS, Ni and Si were found enriched at the cavity surfaces and Ni,Si-rich precipitates were also found. Multivariate statistical analysis using non-negative matrix factorization reveals that these Ni,Si-rich precipitates contain only ∼5.7 at.% Si, differing from the Ni3Si γ’ precipitates found in several previous studies. In X-750, L12-structured γ’ precipitates were found, and multivariate statistical analysis confirmed the 3:1 stoichiometry (Ni3(Ti,Al)) of the γ’ precipitates and the superlattice reflections confirmed the stability of the crystal structure of these γ’ precipitates, indicating higher-than-expected precipitate stability under high-dose neutron irradiation.

Original languageEnglish (US)
Article number151851
JournalJournal of Nuclear Materials
Volume528
DOIs
StatePublished - Jan 2020

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Keywords

  • Frank loops
  • Neutron irradiation
  • Nickel-base alloys
  • Stainless steel
  • Superlattice reflection
  • Transmission electron microscopy (TEM)

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Materials Science(all)
  • Nuclear Energy and Engineering

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