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

Structured keywords

  • Cabot Institute Low Carbon Energy Research

Keywords

  • fusion
  • martensite
  • microstructure
  • thermal effects
  • modelling

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