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

doi:10.1016/j.jnucmat.2021.153084

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

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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 language	English
Article number	153084
Number of pages	14
Journal	Journal of Nuclear Materials
Volume	554
Early online date	19 May 2021
DOIs	https://doi.org/10.1016/j.jnucmat.2021.153084
Publication status	Published - 1 Oct 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)

Research Groups and Themes

Cabot Institute Low Carbon Energy Research

Keywords

fusion
martensite
microstructure
thermal effects
modelling

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Kumar, D., Hargreaves, J., Bharj, A., Scorror, A., Harding, L. M., Dominguez Andrade, H., Holmes, R., Burrows, R. W., Dawson, H., Warren, A. D., Flewitt, P. E. J., & Martin, T. L. (2021). The Effects of Fusion Reactor Thermal Transients on the Microstructure of Eurofer-97 Steel. Journal of Nuclear Materials, 554, Article 153084. https://doi.org/10.1016/j.jnucmat.2021.153084

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title = "The Effects of Fusion Reactor Thermal Transients on the Microstructure of Eurofer-97 Steel",

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.",

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

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: {\textcopyright} 2021 The Author(s)",

year = "2021",

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doi = "10.1016/j.jnucmat.2021.153084",

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AU - Kumar, David

AU - Hargreaves, James

AU - Bharj, Amrick

AU - Scorror, Alex

AU - Harding, Lottie M

AU - Dominguez Andrade, Hugo

AU - Holmes, R.

AU - Burrows, Robert W

AU - Dawson, Huw

AU - Warren, A D

AU - Flewitt, Peter E J

AU - Martin, Tomas L

N1 - 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)

PY - 2021/10/1

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N2 - 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.

AB - 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.

KW - fusion

KW - martensite

KW - microstructure

KW - thermal effects

KW - modelling

U2 - 10.1016/j.jnucmat.2021.153084

DO - 10.1016/j.jnucmat.2021.153084

M3 - Article (Academic Journal)

SN - 0022-3115

VL - 554

JO - Journal of Nuclear Materials

JF - Journal of Nuclear Materials

M1 - 153084

ER -

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

Abstract

Bibliographical note

Research Groups and Themes

Keywords

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