Assessment of hydrogen embrittlement behavior in Al-Zn-Mg alloy through multi-modal 3D image-based simulation

Fujihara, Hiro*; Toda, Hiroyuki*; Ebihara, Kenichi; Kobayashi, Masakazu*; Mayama, Tsuyoshi*; Hirayama, Kyosuke*; Shimizu, Kazuyuki*; Takeuchi, Akihisa*; Uesugi, Masayuki*

International Journal of Plasticity, 174, p.103897_1 - 103897_22, 2024/03

https://doi.org/10.1016/j.ijplas.2024.103897

Hydrogen(H) embrittlement in high-strength aluminum(Al) alloys is a crucial problem. H accumulation at the interface of precipitates in Al alloy is considered to cause embrittlement. However, there is no quantitative knowledge regarding the interaction between H distribution and stress field near cracks. In this study, using a multi-modal three-dimensional image-based simulation combining the crystal plasticity finite element method and H diffusion analysis, we tried to capture the stress distribution near the crack, its influence on the H distribution, and the probability of crack initiation in the experimental condition. As a result, it was found that grain boundary cracks transition to quasi-cleavage cracks in the region where the cohesive energy of the semi-coherent interface of MgZn precipitates decreases due to H accumulation near the tip. We believe the present simulation method successfully bridges nanoscale delamination and macroscale brittle fracture.

Multi-modal 3D image-based simulation of hydrogen embrittlement crack initiation in Al-Zn-Mg alloy

Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*

Keikinzoku, 73(11), p.530 - 536, 2023/11

https://doi.org/10.2464/jilm.73.530

In Al-Zn-Mg alloys, suppression of hydrogen embrittlement is necessary to improve their strength. In this study, the distribution of stress, strain, and hydrogen concentration in the actual fracture region was investigated using the crystal plasticity finite element method and hydrogen diffusion analysis based on a model derived from three-dimensional polycrystalline microstructural data obtained by X-ray CT. In addition, the distributions of stress, strain, and hydrogen concentration were compared with the actual crack initiation behavior by combining in-situ observation of tensile tests using X-ray CT and simulation. The results show that stress loading perpendicular to the grain boundary due to crystal plasticity dominates grain boundary crack initiation. It was also found that internal hydrogen accumulation due to crystal plasticity has little effect on crack initiation.

Evaluation and analysis method of hydrogen embrittlement, 3; Interpretation of thermal desorption profiles of hydrogen based on numerical simulations

Ebihara, Kenichi

Zairyo, 71(5), p.481 - 487, 2022/05

https://doi.org/10.2472/jsms.71.481

no abstracts in English

Effects of stress and plastic strain on hydrogen embrittlement fracture of a U-bent martensitic steel sheet

Shibayama, Yuki; Hojo, Tomohiko*; Koyama, Motomichi*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Matsuno, Takashi*; Akiyama, Eiji*

ISIJ International, 61(4), p.1322 - 1329, 2021/04

https://doi.org/10.2355/isijinternational.ISIJINT-2020-569

Numerical interpretation of hydrogen thermal desorption spectra for iron with hydrogen-enhanced strain-induced vacancies

Ebihara, Kenichi; Sugiyama, Yuri*; Matsumoto, Ryosuke*; Takai, Kenichi*; Suzudo, Tomoaki

Metallurgical and Materials Transactions A, 52(1), p.257 - 269, 2021/01

https://doi.org/10.1007/s11661-020-06075-7

We simulated the thermal desorption spectra of a small-size iron specimen to which was applied during charging with hydrogen atoms using a model incorporating the behavior of vacancies and vacancy clusters. The model considered up to vacancy clusters , which is composed of nine vacancies and employed the parameters based on atomistic calculations, including the H trapping energy of vacancies and vacancy clusters that we estimated using the molecular static calculation. As a result, we revealed that the model could, on the whole, reproduced the experimental spectra except two characteristic differences, and also the dependence of the spectra on the aging temperature. By examining the cause of the differences, the possibilities that the diffusion of clusters of and is slower than the model and that vacancy clusters are generated by applying strain and H charging concurrently were indicated.

Hydrogen embrittlement resistance of pre-strained ultra-high-strength low alloy TRIP-aided steel

Hojo, Tomohiko*; Kumai, B.*; Koyama, Motomichi*; Akiyama, Eiji*; Waki, Hiroyuki*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Nagasawa, Akihiko*

International Journal of Fracture, 224(2), p.253 - 260, 2020/08

https://doi.org/10.1007/s10704-020-00451-5

In the study, the pre-strain effect on hydrogen embrittlement property of the ultra-high-strength transformation-induced plasticity -aided bainitic ferrite steel was investigated towards application for automobile frame parts. 3-10% tensile pre-strain suppressed hydrogen-induced mechanical degradation relative to total elongation while 12-15% pre-strained specimen did not exhibit elongation after hydrogen charging. The advantageous effect of the 3-10% pre-strain was attributed to the suppression of crack initiation related to retained austenite. The TRIP by pre-straining decreased the volume fraction of retained austenite before hydrogen charging, thereby reducing existing probabilities of preferential crack initiation sites and propagation paths. Conversely, high pre-strain such as 12-15% does not effectively work due to work hardening resulting in increases in hydrogen embrittlement susceptibility and a significant increase in hydrogen content due to the multiplication of dislocations.

Determination of detrapping and trapping rate constants for hydrogen based on experimental thermal desorption spectra

Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*

Proceedings of 2016 International Hydrogen Conference (IHC 2016); Materials Performance in Hydrogen Environments, p.470 - 477, 2017/00

http://doi.org/10.1115/1.861387_ch53

For understanding hydrogen (H) embrittlement of steels, it is necessary to infer the state that defects trap H in the steels. Thermal desorption spectra of H obtained by the thermal desorption spectrometry (TDS) are used for inferring such a state. Because the thermal desorption spectra include the influence of experimental conditions and hydrogen diffusion as well as information of the defects trapping H, it is necessary to interpret the spectra using the numerical simulation. In the presentation, we determined the detrapping and the trapping rate constants which are necessary for the simulation from the experimental spectra obtained for plate specimens which is so small that H diffusion is ignorable. Then we confirmed that the model using the obtained rate constants can simulate the spectra of larger cylindrical specimens, so that it was found that the rate constant for small specimens can be used for the simulation of the spectra for specimens of different shape or size.

Numerical reproduction of hydrogen thermal desorption spectra of tempered martensitic steel based on experimental data

Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*

"Suiso Zeika No Kihon Yoin, Kaiseki To Hyoka" Shimposium Yokoshu (USB Flash Drive), p.27 - 33, 2015/09

The thermal desorption spectra which reflect the H segregation state can be obtained by heating a specimen including H at a constant rate. However, the simulation of spectra needs to extract information of the H segregation state because spectra is affected by experimental conditions and H diffusion. The detrapping activation energy E and the pre-exponential factor of detraping rate constant which are simulation parameters are fixed from the data previously reported or by fitting experimental spectra. Instead, we evaluated both of them from the experimental spectra of the specimen in which the H diffusion effect can be ignored, and simulated the spectra using them. As a result, in the case of iron, we could simulate spectra better than by the previous parameters. In the case of tempered martensitic steel, we could simulate spectra by the value obtained by adjusting the evaluated p along with the evaluated E.

Atomistic and continuum comparative studies on the stress distribution around a nano-crack on the grain boundary for modeling hydrogen embrittlement of iron

Ebihara, Kenichi; Kaburaki, Hideo; Itakura, Mitsuhiro

"Hagane No Kikaiteki Tokusei Ni Oyobosu Suiso No Koka To Sono Hyoka" Shimpojium Yokoshu (USB Flash Drive), 6 Pages, 2014/09

Since hydrogen(H) embrittlement is one factor causing degradation and/or fracture of steel, understanding its mechanism is required. The grain-boundary(GB) decohesion due to segregation of H is considered to cause the delayed fracture of high strength steels and the cold cracking in welding. In the model based on GB decohesion, information of strength of GBs estimated in the atomic scale is used for the estimation of strength or crack propagation in the macroscopic scale. However the modeling between the atomic and the macroscopic scales is not clear. In particular, the validity of the model using the elastic continuum around nano-cracks for stress concentration at the crack tip is not clear. Thus, we examined the difference of the stress distribution around the nano-crack which was estimated by molecular dynamics and by a continuum calculation. As a result, the discrepancy became remarkable at high strain. The stress concentration was not simulated by the elastic continuum model.

Low activated materials as plasma facing components

Hino, Tomoaki*; Hirohata, Yuko*; Yamauchi, Yuji*; Sengoku, Seio

Proceedings of IAEA 18th Fusion Energy Conference (CD-ROM), 5 Pages, 2001/00

no abstracts in English