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17–22 Oct 2016
Kyoto International Conference Center
Japan timezone

Deuterium retention and melting behavior in Toughened, Fine-Grained Recrystallized Tungsten

20 Oct 2016, 08:30
4h
Kyoto International Conference Center

Kyoto International Conference Center

Takaragaike, Sakyo-ku, Kyoto 606-0001 Japan
Poster MPT - Materials Physics and Technology Poster 5

Speaker

Mr Makoto Oya (JpUOsaka)

Description

Toughened, Fine-Grained Recrystallized Tungsten (TFGR W) has been developed at Tohoku Univ., Japan [1], in order to improve poor mechanical properties of W such as brittleness at low temperature and embrittlement following neutron irradiation. TFGR W has an average grain size of ~1 µm with a small amount of TiC and TaC dispersoids. These features of the microstructure serve to improve ductility. Here we report the performance of TFGR W under hydrogen isotope irradiation conditions and its applicability as a plasma-facing material, with respect to hydrogen isotope retention and melting behavior. First, deuterium (D) retention was investigated. Two types of TFGR W specimens were prepared; TFGR W-1.1wt%TiC and TFGR W-3.3wt%TaC (referred to as W-TiC and W-TaC, respectively). For comparison, pure W specimens were also investigated. D irradiation was conducted using HiFIT at Osaka Univ. [2]. D fluence of ~1 x 10^24 m^-2 was implanted at temperatures of 473 - 873 K. The D retention was determined by TDS. At temperatures above 473 K, D retention in TFGR W is systematically higher than in pure W. The difference is about one order of magnitude at ~573 K, which is close to the water coolant temperature of the W divertor of a recent DEMO concept [3], suggesting that the use of TFGR W could greatly increase tritium retention. At a temperature of 773 K, retained amount of W-TiC is higher than W-TaC. At ~800 K, which corresponds to about surface temperature of ferritic-martensitic steel blankets, W-TaC should be used for reduced retention. Secondly, in order to study their melting behavior, TFGR W specimens were exposed to TEXTOR edge plasmas at temperatures above the melting point. The D plasma parameters were I_p = 350 kA, B_t = 2.25 T and n_e = 3.5 x 10^19 m^-3. Specimen surfaces were molten at the roof limiter position of 46.4 cm. The re-solidified layer of W-TiC has many small pores with size of ~ 1 µm, while that of W-TaC has a dome-like structure with a height of ~500 µm and a few cracks with ~ 1 cm long. These rough layers could lead to increased erosion when loaded by repeated exposure. Therefore, TFGR W should be more improved to mitigate surface roughening under extreme heat flux conditions. [1] H. Kurishita et al., Phys. Scr. T159 (2014) 014032 [2] Y. Ueda et al., Fusion Eng. Design 62 (2002) 255-261 [3] K. Tobita et al., Nucl. Fusion 49 (2009) 075029
Country or International Organization Japan
Paper Number MPT/P5-27

Primary author

Mr Makoto Oya (JpUOsaka)

Co-authors

Dr Arkadi Kreter (DeFJ) Dr Gregory De Temmerman (ITERFr) Dr Heun Tae Lee (JpUOsaka) Dr Hiroaki Kurishita (International Research Center for Nuclear Materials Science, JpUTohoku) Dr Jan Willem Coenen (DeFJ) Dr Kenzo IBANO (JpUOsaka) Dr Makoto Oyaidzu (JpIFERC) Dr Takumi Hayashi (JpIFERC) Dr Thomas Warwick Morgan (NIFOM) Prof. Yoshio Ueda (JpUOsaka)

Presentation materials