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Materials for Fusion Reactors

2015-10-22

Seminar by Professor Wolfgang Pantleon of the Technical University of Denmark

You are cordially invited to attend a seminar by Professor Wolfgang Pantleon of the Technical University of Denmark.

Time: November 6 at 13:00.

Place: Room IP2 at the Division of Industrial Production in the M-Building on the LTH campus.

Abstract
One of the key issues in constructing future fusion reactors is the selection and development of materials being able to withstand the high temperature and the high mechanical and radiation loads that alter the microstructure of the materials. Creation of a preferable microstructure and thermal stability of the achieved result is discussed for two materials proposed for two different purposes in the reactor:

1) Pure tungsten is considered as a preferred candidate material for the plasma-facing first wall and the divertor of future fusion reactors. Both parts have to withstand high temperatures during service. Therefore, the thermal stability of two pure tungsten plates warm-rolled to 67% and 90% thickness reduction was investigated by long-term isothermal annealing for temperatures in the range between 1100°C and
1350°C up to 2200 h. During annealing, recovery and recrystallization processes cause softening of the material, which can be quantified by Vickers hardness measurements. Two characteristic annealing stages are identified and confirmed by microstructural analysis using electron backscatter diffraction. Taking into account the hardness loss during recovery, which is nicely described by logarithmic time dependence, the recrystallized volume fraction is determined quantitatively and the recrystallization
kinetics is analyzed in terms of Johnson Mehl Avrami Kolmogorov kinetics. Activation energies are determined for different thermally activated processes allowing a prediction of the expected life spans: for the 67% warm-rolled material, the activation energies correspond to that of bulk self-diffusion, whereas the activation energies of the 90% warm-rolled plate coincide with that of short circuit diffusion.


2) Oxide dispersion strengthened (ODS) steels are considered to be promising structural materials for the next-generation fission and fusion reactors. Irradiation induced swelling might be reduced in such materials by refining their microstructures, which may therefore exhibit improved irradiation tolerance compared to their coarse-grained counterparts. An efficient way to refine the microstructure is via plastic
deformation when original grains are subdivided by deformation-induced dislocation boundaries. By dynamic plastic deformation to strain of 2.1, nanoscale lamellae with a strong 〈100〉+〈111〉 duplex fibre texture were successfully introduced in PM2000. Upon annealing, preferential recovery and preferential nucleation of recrystallization are both found in the 〈111〉-oriented lamellae, which had a higher stored energy density in the as-deformed condition. In the course of recrystallization, the initial
duplex fibre texture is replaced by a strong 〈111〉-fibre recrystallization texture. Furthermore, plastic deformation of the small nanodispersoids was also discovered.

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