27pB05
TFGR W中の水素同位体挙動
Deuterium Retention in Toughened, Fine-Grained Recrystallized Tungsten
大宅 諒1), 大塚裕介1), 上田良夫1), 栗下裕明2)
OYA Makoto1), OHTSUKA Yusuke1), UEDA Yoshio1), KURISHITA Hiroaki2)
1)大阪大学大学院工学研究科 2)東北大学金属材料研究所
1)Graduate School of Engineering, Osaka Univ. 2)Institute for Material Research, Tohoku Univ.

1. Introduction
Tungsten (W) will be used as a plasma-facing
material (PFM) in future fusion reactor, and in thedivertor of ITER. However, W suffers from poor
mechanical properties such as high ductile to brittle
temperature resulting in room temperature brittlenessor neutron irradiation embrittlement.
To improve W mechanical properties, a variety ofadvanced W materials have been or are currently underdevelopment. One such material is TFGR W(Toughened,Fine-Grained
RecrystallizedW)developed by Kurishita at Tohoku University [1].
TFGR W has an average grain size of ~1 μm with asmall amount of TiC or TaC dispersoids. Since TFGR
W has enhanced toughness compared to other W
materials, it is expected that it would improve poor
irradiation brittleness of pure W. However, concerningplasma wall interaction issues such as tritium retention
under plasma exposure, TFGR W has limited data sofar.
In this study, we investigated deuterium (D)retention in TFGR W-1.1wt%TiC and TFGR
W-3.3wt%TaC by ion beam implantation followed bythermal desorption in order to increase the D retention
database of TFGR W and clarify D retention
mechanisms.
2. Experiment
TFGR W-1.1wt%TiC and TFGR W-3.3wt%TaC
specimens of 10 x 10 x 1 mm size were used. The D
implantation into TFGR W specimens was conductedusing High-Flux ion beam Irradiation Test device(HiFIT) in Osaka University [2], with an incident
energy of 1keV, and flux density of ~1 x 1020 m-2s-1.
Deuterium fluence of up to about 1 x 1024 m-2 wasimplanted at temperatures of 473 – 873 K. Following
implantation, D retention was measured by thermal
desorption spectroscopy (TDS) in a separate apparatus.
For comparison, the experiments were also made withpure W specimens under the same conditions. Inaddition to pure D implantation, experiments withsome impurity concentration in D ion beam were also
conducted.

3. Results and Discussion
It was found that D retention in both TFGR
W-1.1wt%TiC and TFGR W-3.3wt%TaC specimens
was systematically higher than that of pure W
specimens at all irradiation temperature. In addition, D
retention in TFGR W decreases with temperature more
slowly than pure W. This suggests that TFGR W hastrapping sites with higher trapping energies than thosein pure W. The trap sites could be TiC or TaC
dispersoids, which has chemical affinity with D atoms.
It was also found that D retention in TFGR
W-3.3wt%TaC was lower than that of TFGR
W-1.1wt%TiC at high temperature of 773K, while noapparent difference between retention of these two
specimens at 573 – 673 K. This could be originatedfrom different types of dispersoids of TiC and TaC.
One possible explanation is difference of chemicalcomposition of hydrogen isotopes that Ti or Ta madechemical bonding with D atoms into TiD2 or TaD.
In this presentation, we will discuss the role ofdispersoids (TiC or TaC) and crystalline structure on D
retention in the TFGR W materials.

Figure.1 Temperature dependence on D retention in W
materials (pure W, TFGR W-1.1wt%TiC and TFGR
W-3.3wt%TaC)
Referance[1] H. Kurishita et al., J. Nucl. Mater. 398 (2010)87-92.
[2] Y. Ueda et al., Fusion Eng. Design 62 (2002)
255-261.