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Development of Short-Range Order and Intergranular Carbide Precipitation in Alloy 690 TT upon Thermal Ageing

  • Roman MouginotEmail author
  • Teemu Sarikka
  • Mikko Heikkilä
  • Mykola Ivanchenko
  • Unto Tapper
  • Ulla Ehrnstén
  • Hannu Hänninen
Conference paper
Part of the The Minerals, Metals & Materials Series book series (MMMS)

Abstract

Thermal ageing promotes intergranular carbide precipitation and atomic ordering reaction in most commercial nickel-base alloys, and it affects the long-term primary water stress corrosion cracking (PWSCC) resistance of pressurized water reactor components. Alloy 690 with 9.8 wt% Fe was solution annealed and heat-treated at low temperature, then aged between 350 and 550 °C for 10,000 h. No direct observation of ordering was possible, but variations in hardness and lattice parameter suggested the formation of short-range ordering (SRO) with a peak level upon ageing at 420 °C, while a disordering reaction occurred at higher temperatures. Heat treatment induced ordering before thermal ageing was compared to the solution-annealed state. Thermal ageing resulted in the precipitation of Cr-rich M23C6 carbides at grain boundaries and twin boundaries. Although no link between SRO and an increase in strain localization was observed, the combination of intergranular carbide formation and SRO over longer ageing times was deemed detrimental to the PWSCC resistance of Alloy 690 TT.

Keywords

Alloy 690 Thermal ageing Short-range ordering Ni2Cr Cold work Thermal treatment 

Notes

Acknowledgements

Samples were aged and provided by the Korea Atomic Energy Research Institute (KAERI). The authors wish to thank Prof. Young Suk Kim and Sung Soo Kim from KAERI for initiating the study and providing the Alloy 690 materials. The study was carried out at Aalto University and VTT within the “Thermal ageing and EAC research for plant life management” (THELMA) project of the Finnish Research Programme on Nuclear Power Plant Safety 2015–2018 (SAFIR 2018). XRD measurements were performed at the Helsinki University, Laboratory of Inorganic Chemistry.

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Copyright information

© The Minerals, Metals & Materials Society 2019

Authors and Affiliations

  • Roman Mouginot
    • 1
  • Teemu Sarikka
    • 1
  • Mikko Heikkilä
    • 2
  • Mykola Ivanchenko
    • 3
  • Unto Tapper
    • 3
  • Ulla Ehrnstén
    • 3
  • Hannu Hänninen
    • 1
  1. 1.Department of Mechanical EngineeringAalto University School of EngineeringEspooFinland
  2. 2.Department of ChemistryUniversity of HelsinkiHelsinkiFinland
  3. 3.VTT Technical Research Centre of Finland Ltd.EspooFinland

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