Grain-boundary phosphorus segregation in highly neutron-irradiated reactor pressure vessel steels and its effect on irradiation embrittlement

Hata, Kuniki; Takamizawa, Hisashi; Hojo, Tomohiro*; Ebihara, Kenichi; Nishiyama, Yutaka; Nagai, Yasuyoshi*

Journal of Nuclear Materials, 543, p.152564_1 - 152564_10, 2021/01

https://doi.org/10.1016/j.jnucmat.2020.152564

Reactor pressure vessel (RPV) steels for pressurized water reactors (PWRs) with bulk P contents ranging from 0.007 to 0.012wt.% were subjected to neutron irradiation at fluences ranging from 0.3 to 1.210 n/cm (E 1 MeV) in PWRs or a materials testing reactor (MTR). Grain-boundary P segregation was analyzed using Auger electron spectroscopy (AES) on intergranular facets and found to increase with increasing neutron fluence. A rate theory model was also used to simulate the increase in grain-boundary P segregation for RPV steels with a bulk P content up to 0.020wt.%. The increase in grain-boundary P segregation in RPV steel with a bulk P content of 0.015wt.% (the maximum P concentration found in RPV steels used in Japanese nuclear power plants intended for restart) was estimated to be less than 0.1 in monolayer coverage at 1.010 n/cm (E 1 MeV). A comparison of the PWR data with the MTR data showed that neutron flux had no effect upon grain-boundary P segregation. The effects of grain-boundary P segregation upon changes in irradiation hardening and ductile-brittle transition temperature (DBTT) shifts were also discussed. A linear relationship between irradiation hardening and the DBTT shift with a slope of 0.63 obtained for RPV steels with a bulk P content up to 0.026wt.%, which is higher than that of most U.S. A533B steels. It is concluded that the intergranular embrittlement is unlikely to occur for RPV steels irradiated in PWRs.

Molecular dynamics study of phosphorus migration in 5 grain boundary of -iron

Ebihara, Kenichi; Suzudo, Tomoaki

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.65 - 69, 2020/10

Phosphorus (P) is known as one of the elements which cause the grain boundary (GB) embrittlement in steels and its GB segregation is promoted by the increase of vacancies and self-interstitial atoms due to irradiation. Thus we have been developing the rate-theory model for estimating GB P segregation under several temperatures and irradiation conditions. Because the model does not include the trapping and de-trapping processes properly, however, the model cannot calculate GB P coverage which is measured by experiments. As for the de-trapping process, so far, we have considered the migration of a P atom in the GB region of 3 symmetrical tilt GB using molecular dynamics (MD). In the current study, we also simulated the P migration in 5 GB using MD and compared the result with that of 3. As a result, at 800K, it was found that a P atom cannot migrate in 5 without vacancies while a P atom can migrate between iron atoms in 3.

Austenite-based stainless steel irradiation behavior of the precipitate and void swelling

Inoue, Toshihiko; Sekio, Yoshihiro; Watanabe, Hideo*

Materia, 58(2), P. 92, 2019/02

https://doi.org/10.2320/materia.58.92

For the evaluation of irradiated segregation behavior, Austenite-based stainless steel for the fast reactor, during irradiation was evaluated by utilizing TIARA facility (Irradiate temperature: 600 C, Dose: 100 dpa) was observed by analytical electron microscope (JEM-ARM20FC). As a result of observation, the large-size void is observed in irradiation area, and MX segregation (containing Niobium) is not observed. In un-irradiation area the MX segregation is observed. And it is observed conspicuously that Nickel is segregation on the void surface. By the latest high-performance TEM utilization, these phenomenon are able to visualize. It is expected for the clarification of the irradiation damage and mechanism of void swelling, by the analyzing these phenomenon utilization with the latest high-performance TEM utilization.

Radiation enhanced precipitation of solute atoms in AlCu binary alloys; Energetic ion irradiation experiment and computer simulation

Mayumi, Ren*; Semboshi, Satoshi*; Okamoto, Yoshihiro; Saito, Yuichi*; Yoshiie, Toshimasa*; Iwase, Akihiro*

Transactions of the Materials Research Society of Japan, 42(1), p.9 - 14, 2017/02

https://doi.org/10.14723/tmrsj.42.9

AlCu binary alloys were irradiated with 16 MeV Au, 4.5 MeV Ni or 4.5 MeV Al ions at room temperature. Changes in surface hardness and the local atomic structure around Cu atoms were examined by using the Vickers hardness measurement and the EXAFS measurements, respectively. Some specimens were aged at 453 K and Vickers hardness was measured. The computer simulation was also performed by using the rate equation method. The hardness of irradiated specimens increased much faster than that of the aged specimens and it became larger than the maximum value of the hardness for the aged specimens. The comparison of the experimental EXAFS result with that of FEFF simulation suggests that the ion irradiation produced small Cu precipitates in the specimens. The computer simulation visualized the growth process of Cu precipitates during the irradiation, and the result qualitatively corresponds to the experimental result.

Investigation of segregation during oxidation of Ni-Cu alloy by photoelectron spectroscopy

Doi, Takashi*; Nishiyama, Yoshitaka*; Yoshigoe, Akitaka; Teraoka, Yuden

Surface and Interface Analysis, 48(7), p.685 - 688, 2016/07

https://doi.org/10.1002/sia.6001

Ni-based alloys has been widely used for plant application because of their high strength and excellent oxidation resistance. In particular, the addition of Cu in Ni-based alloys significantly improves the metal dusting resistance. It is indicated that Cu is segregated on the alloy surface in the metal dusting environment; however, the details have not been clarified yet. The behavior of Ni-2Cu alloy under a high temperature oxidation environment was investigated using X-ray photoelectron spectroscopy. It was confirmed that Cu have been segregated at the surface of Ni-2Cu alloy during oxidation. These results propose that the Cu segregation improves the metal dusting resistance.

Response to comment on "Grain Boundary Decohesion by Impurity Segregation in a Nickel-Sulfur System"

Yamaguchi, Masatake; Shiga, Motoyuki; Kaburaki, Hideo

Science, 309(5741), P. 1677d, 2005/09

Geng et al. claim in their comment that the segregation energy of sulfur atoms in a nickel grain boundary should be calculated not on average as we did but incrementally. From their own calculations using the incremental binding energies, they concluded that the two-monolayer (GB0 4/4, GB2 4/4) segregation that bring about the reduction of the tensile strength by one order of magnitude has only 1% occupation possibility. However, they miss the point that there are many paths to the (GB0 4/4, GB2 4/4) configuration. In our re-examined calculations, one path has the 50% possibility of the occupation even if we use the incremental binding energies. Furthermore, there may be other paths that have larger possibility. To begin with, Geng et al.'s claims are not meaningful because the prediction of the occupation possibility using the simple McLean's model is not quantitative but qualitative. On the other hand, they claim that another two-monolayer (GB1 4/4, GB2 4/4) configuration brings about the reduction of the tensile strength by one order of magnitude. Their results may be miscalculations, because that is not the case in our re-examined calculations. Furthremore, they suggest a new mechanism of the strong decohesion due to the directional change of the Ni-S bonds. However, they do not show any clear evidence.

Energetics of segregation and embrittling potency for non-transition elements in the Ni 5 (012) symmetrical tilt grain boundary; A First-principles study

Yamaguchi, Masatake; Shiga, Motoyuki; Kaburaki, Hideo

Journal of Physics; Condensed Matter, 16(23), p.3933 - 3956, 2004/06

https://doi.org/10.1088/0953-8984/16/23/013

A series of non-transition elements bound to the Ni 5(012) symmetrical tilt grain boundary (GB) and the (012) free surface (FS) systems has been studied by first-principles calculation using WIEN2k code. The multilayer relaxations in presence/absence of the solutes are determined by the force minimization. The binding energies at some GB/FS/bulk sites including both interstitial and substitutional sites are calculated for all the non-transition elements between H and Rn. The GB/FS segregation energy is obtained by calculating the binding energy difference between the GB/FS site and the bulk site. The embrittling potency energy is obtained by calculating the difference between the GB and FS segregation energies based on Rice-Wang model. Our results show that most of the non-transition elements have negative GB/FS segregation energies. Here, this means that there exists a segregation site in the GB/FS. The embrittling potency energies are positive for most of the solutes. However, some exceptions like Be, B, C, and Si having negative and large embrittling potency can enhance the GB cohesion. Our results are found to be consistent with the experimental findings.

Corrosion behavior of stainless steels simulating radiation-induced segregation

Miwa, Yukio; Tsukada, Takashi

Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2003, p.301 - 306, 2003/00

Local composition change at grain boundaries due to radiation-induced segregation (RIS) followed by loss of corrosion resistance is considered to be a key mechanism on irradiation-assisted stress corrosion cracking (IASCC). However it is not clear that the local composition change induces the loss of corrosion resistance at grain boundaries, because RIS results in not only depletion of Cr but also enrichment of Ni and Si. This chemical composition change is different from that of thermally-sensitized stainless steels. In this study, experimental alloys were manufactured simulating the composition at grain boundaries of irradiated type 304 stainless steel and corrosion behavior of the experimental alloys was examined by weight loss measurement in 573 K water and anode polarization measurement in 1N sulfuric acid and 1mol/l sodium sulfate at 303 K. Following results were obtained: (1) In oxygenated water (DO=10ppm) at 573 K, weight loss increased with decreasing the concentration of Cr and did not depend on the concentration of Ni and Si. (2) Results of anode polarization measurements showed that alloys contained lower Cr and higher Ni and Si concentration exhibited lower corrosion potential in oxygenated, lower pH solution. In de-aerated solutions both sulfuric acid and sodium sulfate, however, there was a little influence of chemical composition on the corrosion potential.

None

*

JNC TN1400 2001-013, 70 Pages, 2001/08

JNC-TN1400-2001-013.pdf:5.13MB

no abstracts in English

None

Yamanaka, Shinsuke*; Uno, Masayoshi*; Kurosaki, Ken*; ; Namekawa, Takashi

JNC TY9400 2000-011, 41 Pages, 2000/03

JNC-TY9400-2000-011.pdf:1.28MB

no abstracts in English