The Effects of Fusion Reactor Thermal Transients on the Microstructure of Eurofer-97 Steel

David Kumar*, James Hargreaves, Amrick Bharj, Alex Scorror, Lottie M Harding, Hugo Dominguez Andrade, R. Holmes, Robert W Burrows, Huw Dawson, A D Warren, Peter E J Flewitt, Tomas L Martin

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

Plasma-wall interactions in a commercial-scale fusion power station may exert high transient thermal loads on plasma-facing surfaces, repeatedly subjecting underlying structural materials to high temperatures for short durations. Specimens of the reduced activation ferritic-martensitic steel Eurofer-97 were continuously aged at constant temperature in the range of 550ºC to 950ºC for up to 168 hours in a furnace to investigate the microstructural effects of short-term high temperature exposure. A CO2 laser was also used to repeatedly heat another specimen from 400ºC to 850°C a total of 1,480 times over a period of 41 hours to explore transient heating effects. Microstructural changes were studied via scanning electron and focused ion beam microscopy and include (i) the coarsening of Cr-rich secondary phase precipitates when continuously heated above 750°C, (ii) an increase in average grain size above 800ºC and (iii) the evolution of a new lath martensite microstructure above 850ºC. Conversely, transient heating via a laser was found to result in the decomposition of the as-received lath martensite structure into ferrite and Cr-rich carbide precipitates, accompanied by a significant increase in average grain size from 0.1-2 µm to 5-40 µm. Experimental analysis was supported by thermodynamic simulation of the equilibrium phase behaviour of Eurofer-97 in MatCalc and thermal finite element modelling of plasma-wall interaction heating on the water-cooled lithium-lead tritium breeding blanket concept in Comsol Multiphysics. Simulated thermal transients were found to significantly alter the microstructure of Eurofer-97 and the implications of this are discussed.
Original languageEnglish
Article number153084
Number of pages14
JournalJournal of Nuclear Materials
Volume554
Early online date19 May 2021
DOIs
Publication statusE-pub ahead of print - 19 May 2021

Bibliographical note

Funding Information:
The authors would like to thank UKAEA/CCFE for the provision of a representative specimen of Eurofer-97. D. Kumar would like to thank EPSRC and NNL for the funding of his doctoral training partnership PhD project ( S108151-136 ), and J. Hargreaves would like to thank the Centre for Doctoral Training in Nuclear Energy Futures for funding his PhD (UK EPSRC grant EP/S023844/1). Dr Neil Fox, Dr James Smith and Mr Gary Wan are thanked for their assistance with the laser apparatus. Dr Fabio Moro is thanked for providing design data and drawings of the WCLL.

Funding Information:
The authors would like to thank UKAEA/CCFE for the provision of a representative specimen of Eurofer-97. D. Kumar would like to thank EPSRC and NNL for the funding of his doctoral training partnership PhD project (S108151-136), and J. Hargreaves would like to thank the Centre for Doctoral Training in Nuclear Energy Futures for funding his PhD (UK EPSRC grant EP/S023844/1). Dr Neil Fox, Dr James Smith and Mr Gary Wan are thanked for their assistance with the laser apparatus. Dr Fabio Moro is thanked for providing design data and drawings of the WCLL.

Publisher Copyright:
© 2021 The Author(s)

Structured keywords

  • Cabot Institute Low Carbon Energy Research

Keywords

  • fusion
  • martensite
  • microstructure
  • thermal effects
  • modelling

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