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247 results on '"Wu, Xuebang"'

6. Magnetic ordering phase transition and abnormal brittleness in dilute Fe-Mn solid solution

Author

Liu, Wei, Liang, Yunfeng, Li, Xiangyan, Xu, Yichun, Zhang, Yange, Li, Wenliang, Fang, Q. F., Miranda, Caetano R., Yang, Chuan-Lu, Liu, C. S., and Wu, Xuebang

Subjects
Condensed Matter - Materials Science
Abstract

Experiments showed that solute Mn in bcc iron is in antiferromagnetic (AFM) coupling with iron neighbours below 2 at.% Mn, but is in ferromagnetic (FM) coupling at higher concentrations. Surprisingly, although Mn is an important alloying element in high-strength steels, it induces brittleness just at around 2 at.% Mn and higher concentrations. However, the mechanisms for the magnetic ordering phase transition and the abnormal brittleness remain unclear. Based on magnetism-constrained/unconstrained calculations and ab initio molecular dynamics simulations within density functional theory, we show that while the AFM phase prevails at low Mn contents, the FM phase becomes dominant at 1.85 at.% Mn and elevated temperatures. Our results suggest that the AFM-FM phase transition with increasing Mn concentration can be ascribed to the thermal effect. Furthermore, we find that the brittleness of the Fe-Mn alloys at intermediate Mn content might be related to the stress variations within the grains accompanying the local magnetic ordering changes., Comment: 31 pages, 4 figures

Published
2021

17. Predictive Model of Hydrogen Trapping and Bubbling in Nanovoids in BCC Metals

Author

Hou, Jie, Kong, Xiang-Shan, Wu, Xuebang, Song, Jun, and Liu, C. S.

Subjects
Condensed Matter - Materials Science, Physics - Computational Physics
Abstract

Interplay between hydrogen and nanovoids, despite long-recognized as a central aspect in hydrogen-induced damages in structural materials, remains poorly understood. Focusing on tungsten as a model BCC system, the present study, for the first time, explicitly demonstrated sequential adsorption of hydrogen adatoms on Wigner-Seitz squares of nanovoids with distinct energy levels. Interaction between hydrogen adatoms on the nanovoid surface is shown to be dominated by pairwise power law repulsion. A predictive model was established for quantitative prediction of configurations and energetics of hydrogen adatoms in nanovoids. This model, further combined with equation of states of hydrogen gas, enables prediction of hydrogen molecule formation in nanovoids. Multiscale simulations based on the predictive model were performed, showing excellent agreement with experiments. This work clarifies fundamental physics and provides full-scale predictive model for hydrogen trapping and bubbling in nanovoids, offering long-sought mechanistic insights crucial for understanding hydrogen-induced damages in structural materials.

Published
2018
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20. Hydrogen bubble nucleation by self-clustering: Density Functional Theory and statistical models studies using tungsten as a model system

Author

Hou, Jie, Kong, Xiang-Shan, Sun, Jingjing, You, Yu-Wei, Wu, Xuebang, liu, C. S., and Song, Jun

Subjects
Condensed Matter - Materials Science
Abstract

Low-energy hydrogen irradiation is known to induce bubble formation in tungsten, while its atomistic mechanisms remain little understood. Using first-principles calculations and statistical models, we studied the self-clustering behavior of hydrogen in tungsten. Unlike previous speculations that hydrogen self-clusters are energetically unstable owing to the general repulsion between two hydrogens, we demonstrated that hydrogen self-cluster becomes more favorable as the cluster size increases. We found that hydrogen atoms would form two-dimensional platelet-like structures along {100} planes. These hydrogen self-clustering behaviors can be quantitative understood by the competition between long-ranged elastic attraction and local electronic repulsion. Further statistical analysis showed that there exists a critical hydrogen concentration above which hydrogen self-clusters are thermodynamically stable and kinetically feasible. Based on this critical hydrogen concentration, the plasma loading conditions under which hydrogen self-clusters form were predicted. Our predictions showed excellent agreement with experimental results of hydrogen bubble formation in tungsten exposed to low-energy hydrogen irradiation. Finally, we proposed a possible mechanism for the hydrogen bubble nucleation via hydrogen self-clustering. This work provides mechanistic insights and quantitative models towards understanding of plasma-induced hydrogen bubble formation in plasma-facing tungsten., Comment: 21 pages, 8 figures, regular article

Published
2017
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34. Surface modification of ZrC dispersion-strengthened W under low energy He plasma irradiation.

Author

Li, Long, Liu, Zhe, Chen, Ze, Yin, Chao, Mao, Shifeng, Wu, Xuebang, Ohno, Noriyasu, and Ye, Minyou

Subjects
IRRADIATION, HIGH temperature plasmas, THERMAL shock, SPUTTER deposition, TRANSITION temperature, MATERIAL erosion, THERMAL resistance
Abstract

ZrC dispersion-strengthened W exhibits high strength/ductility, low ductile-to-brittle transition temperature, and excellent thermal shock resistance, making it a promising candidate plasma-facing material for future fusion devices. In this study, surface modification of 0.5 wt.% ZrC dispersion-strengthened W (WZrC) under low energy and high fluence He plasma irradiation at high temperature was presented. Under the energy of 90 eV and fluence ranging from 6 × 1024 He·m−2–2 × 1026 He·m−2 He irradiation at 920 °C, a typical fuzz nanostructure appeared on the W matrix of WZrC. The thickness of fuzz layer is proportional to the square root of He irradiation fluence. The fuzz showed comparable thickness and structural features to pure W, indicating limited effects of the particle's addition on resistance to high fluence He irradiation at high temperatures. Under continuous He injection, the fuzz would grow extending onto the particle area, making the particle obscured. Besides, the erosion behavior of particles under He plasma irradiation has been investigated, which is thought to be dominated by a sputtering process. Under the He influence of 6 × 1024 He·m−2, only nanopores were observed in the surface region. With fluence increasing to 5 × 1025 He·m−2, the surface became relatively uneven with larger holes. W aggregated in spots and distributed on the surface of the particle, which might be the result of subthreshold sputtering and deposition. When fluence further increased to 2 × 1026 He·m−2, the particles were eroded completely and covered by the extended fuzz, forming cavities. In addition, distinctive layered nanotendrils were observed above the cavities, which were characterized to consist of inner W-riched skeletons and outer Zr-riched layers. It indicates that the layered nanotendrils should be the result of fuzz extension combined with particle sputtering/deposition. [ABSTRACT FROM AUTHOR]

Published
2024
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45. Microstructure Characterization and Hardening Evaluation of Ferrite/Martensitic Steels Induced by He 2+ Irradiation.

Author

Zhang, Guangjie, Yang, Junfeng, Xie, Zhuoming, Zhang, Linchao, Liu, Rui, Sun, Meng, Li, Gang, Wang, Hui, Hu, Yi, Wu, Xuebang, Fang, Qianfeng, Liu, Changsong, and Wang, Xianping

Subjects
DISLOCATION loops, IRRADIATION, FERRITES, DISPERSION strengthening, STEEL, TRANSMISSION electron microscopy, NEUTRON irradiation, MICROSTRUCTURE
Abstract

Two ferrite/martensitic (F/M) steels with different Si concentrations (0 and 0.4 wt.%) were irradiated by 250 keV He2+ ions with different fluences of 2 × 1016 ions/cm2 and 1 × 1017 ions/cm2. Transmission electron microscopy and a nanoindenter were employed to investigate their microstructure evolution and irradiation hardening effects induced by high-energy He2+ ions. A large number of He bubbles formed in the Si-free and Si-containing F/M steels, which preferentially nucleated and grew at the lath and phase boundaries. Owing to the inhibiting effect of Si addition on He bubble growth, the He bubbles in the Si-containing sample exhibited smaller size and higher density at the same He2+ fluence. Nanoindenter measurement revealed that typical irradiation hardening was observed in the F/M steel, and 1/2<111> and <100> type dislocation loops formed by He2+ irradiation was recognized as the dominant mechanism. The addition of Si induced an increase in the number density of dislocation loops, leading to the exacerbation of the irradiation hardening, and the results are basically in agreement with the theoretical analysis based on the dispersion barrier hardening (DBH) and Friedel–Kroupa–Hirsch (FKH) models. [ABSTRACT FROM AUTHOR]

Published
2023
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49. Mechanical Spectroscopy: Some Applications On Structural Changes And Relaxation Dynamics In Soft Matter

Author

Wu Xuebang and Liu Changsong

Subjects
Polymer segmental dynamics, colloids, granular matter, mechanical spectroscopy, Mining engineering. Metallurgy, TN1-997, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

The general trend in soft matter is to study systems of increasing complexity covering a wide range in time and frequency. Mechanical spectroscopy is a powerful tool for understanding the structure and relaxation dynamics of these materials over a large temperature range and frequency scale. In this work, we collect a few recent applications using low-frequency mechanical spectroscopy for elucidating the structural changes and relaxation dynamics in soft matter, largely based on the author’s group. We illustrate the potential of mechanical spectroscopy with three kinds of soft materials: colloids, polymers and granular systems. Examples include structural changes in colloids, segmental relaxations in amorphous polymers, and resonant dissipation of grain chains in three-dimensional media. The present work shows that mechanical spectroscopy has been applied as a necessary and complementary tool to study the dynamics of such complex systems.

Published
2015
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