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Oka, Hiroshi; Tanno, Takashi; Yano, Yasuhide; Otsuka, Satoshi; Kaito, Takeji; Tachi, Yoshiaki
Journal of Nuclear Materials, 547, p.152833_1 - 152833_7, 2021/04
Times Cited Count：7 Percentile：75.99(Materials Science, Multidisciplinary)In order to evaluate the stability of nano-sized oxide particles and matrix structure of ODS cladding tube, which are the determinants of their high temperature strength, the microstructural observation was carried out after internal pressurized creep test at 700
C for over 45,000 hours. The specimens were the as-received and crept specimens of 9Cr-ODS steel with tempered martensite and 12Cr-ODS steel with recrystallized ferrite. Small platelet was cut out from the crept pressurized tube, then thinned to foil. Microstructural observation was conducted with TEM JEOL 2010F. As a result of the observation, it was confirmed that the size and number density of the nano-sized particles were almost unchanged even after the creep test. In addition, the tempered martensite structure, which is one of the determinants of the creep strength of 9Cr-ODS steel, was not significantly different between the as-received and crept specimen, indicating the stability of their matrix structure.
Yano, Yasuhide; Tanno, Takashi; Oka, Hiroshi; Sekio, Yoshihiro; Otsuka, Satoshi; Kaito, Takeji; Tachi, Yoshiaki
no journal, ,
Ferritic/martensitic (F/M) steels are expected to be used not only for the long-life core material of fast reactors, but also for the blanket materials of fusion reactor due to their superior swelling resistance. It is important to evaluate the mechanical properties of the dissimilar joints after thermal aging. The present study evaluated and discussed the effect on the tensile properties of EB welded dissimilar joints produced by thermal aging up to 30000 h. Most welds were overmatched for all aging conditions and ultimate tensile strength of aged WM were higher than those of aged base metals (PNC-FMS and 316SS. UTS of the WM aged at 400C was about 1.5 times higher than that of as-received WM (1100 MPa), but there was no significant change in the uniform elongation before and after aging. The Cr-rich phase were observed in a part of WM areas after thermal aging at 400 and 450C. The Cr-rich phase at 400C was finer and more homogenous than those at 450C.
Tanno, Takashi; Yano, Yasuhide; Oka, Hiroshi; Sekio, Yoshihiro; Otsuka, Satoshi; Kaito, Takeji; Tachi, Yoshiaki
no journal, ,
Ferritic/martensitic (F/M) steels are candidate for core material of fast reactors (FR) because of its superior swelling resistance. A 11Cr F/M steel (PNC-FMS) have been developed for wrapper tube and cladding tube for FR in JAEA. For demonstration of in-reactor performance and preparation of material strength standard, it is important to extend database on irradiation and thermal aging effects. In this work, ring tensile tests and hardness tests of PNC-FMS irradiated in Joyo up to 32.5 dpa at 455-835 C were carried out, and the results were compared with those of aging tests to clarify the irradiation effects exclusive of thermal aging effects. The UTS and hardness at RT of PNC-FMS irradiated at over 600 C tended to be lower than those of as-received and/or thermal aged ones. The facts indicate evident irradiation softening. On the other hand, PNC-FMS irradiated at 835 C was harder than that of aged one. Transformation during irradiation would be the cause.
Konno, Azusa; Oba, Yojiro; Tominaga, Aki; Morooka, Satoshi; Ono, Naoko*; Hashimoto, Naoyuki*; Ukai, Shigeharu; Owada, Kenji*; Motokawa, Ryuhei; Kumada, Takayuki; et al.
no journal, ,
An ODS alloy is one of the promising candidate materials applicable to the fusion reactor because of its high-temperature creep strength and irradiation resistance. However, the ODS ferritic stainless steel with high Cr content sometimes suffers from the embrittlement related to phase separation below 748 K for a long term using in the reactor. It is, therefore, an important issue to understand embrittlement phenomena from not only macrostructural viewpoint but also microstructural one. Anomalous Small Angle X-ray Scattering (A-SAXS) is a unique and potential evaluation method that can analyze complex microstructure. This method can extract the signal only from an element of interest to implant the X-ray of the wavelength near orbit electron of the element. In this study, we performed both the A-SAXS analysis and TEM observation for high Cr-ODS alloy in order to assess the applicability of the A-SAXS technique as a microstructure determination and compared the A-SAXS signal with the TEM micrograph. The specimen of the commercial MA956 (Fe-20Cr-4.8Al-0.4Ti-0.02C-0.4Y
O
(mass%)) were thermally-aged at 748 K for 1, 10, 100 and 1000 hrs, and measured using the A-SAXS diffractometer at BL22XU in SPring-8 and a TEM. The A-SAXS data reveal that the average size of Cr precipitations increases with increasing the aging time. Also, using the A-SAXS profiles, it was estimated that there were two cases; one is the case that the microstructure does have a distinct interface between the matrix and Cr precipitate. The other case is the microstructure does not have the distinct interface. On the other hand, in TEM observation, the periodic modulated structure was observed for 10 hrs thermally-aged sample, and the sphere precipitation was confirmed for 100 hrs thermally-aged sample. It was suggested that there would be a crucial phase separation mode from spinodal decomposition to nucleation-growth between 10 and 100 hrs.
Tsuru, Tomohito; Suzudo, Tomoaki; Itakura, Mitsuhiro; Wakeda, Masato*; Ogata, Shigenobu*
no journal, ,
Effect of transmutation products such as Re and Os is one of the central issues on change in mechanical properties under neutron irradiation in fusion reactors. Especially, Re solutes in W affect not only hardening via radiation-induced precipitation but also significant softening effect. We explored softening/strengthening behavior in various solutes in W matrix by density functional theory (DFT) calculations combined with a solid solution model. In addition, we proposed a method for the dynamics motion of a screw dislocation based on kink nucleation and kink migration, in which Hamiltonian of a dislocation is described by line tension model. As a result of DFT calculations for various solutes, a clear trend was observed in the interaction energy between a solute and a screw dislocation, which has predominant influence on solid solution behavior.
Abe, Yosuke; Sato, Yuki*; Okubo, Nariaki; Konno, Azusa
no journal, ,
We examined a role of 1D migration of SIA clusters in their nucleation and growth behavior in electron-irradiated alpha-iron below 300 K. Using 1D random walk theory, we derived the analytical expression of trapping probability of SIA clusters by impurity atoms within a foil specimen. By incorporating this modelinto a reaction rate theory, it was shown that the saturated cluster number density significantly decreases due to the decrease in the cluster nucleation rate. Also, the dependence of the irradiation beam intensity on the saturated cluster number density becomes weaker when the absorption probability of one-dimensionally migrating SIA clusters by other stationary SIA clusters is higher than the trapping probability by impurity atoms. The irradiation-induced detrapping increases the annihilation rate of the liberated SIA clusters at specimen surfaces, leading to the decrease in the cluster number density at higher irradiation doses, as observed experimentally.
