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学者姓名：韩卫忠
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Abstract ：
Ductile-to-brittle transition (DBT) is a well-known phenomenon in body-centered-cubic (BCC) metals, intermetallics and semiconductor materials. A quantitative prediction of the DBT temperature, however, has so far remained intractable. Here, we propose a unified model based on the efficacy of dislocation multiplication as the controlling factor for DBT, with the dislocation source efficiency governed by the relative mobility of screw versus edge dislocations. The model successfully predicts the DBT temperature of iron, molybdenum and tungsten, and also covers the influence of grain size, initial dislocation density, and the multiplicity of dislocation sources. A comparison with experiments indicates that the model captures the key DBT features, providing new insight into the toughness of BCC metals. © 2022
Keyword ：
Brittle; Dislocation; Ductile; Metals; Mobility
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| GB/T 7714 | Zhang, Y.-H. , Ma, E. , Sun, J. et al. A unified model for ductile-to-brittle transition in body-centered cubic metals [J]. | Journal of Materials Science and Technology , 2023 , 141 : 193-198 . |
| MLA | Zhang, Y.-H. et al. "A unified model for ductile-to-brittle transition in body-centered cubic metals" . | Journal of Materials Science and Technology 141 (2023) : 193-198 . |
| APA | Zhang, Y.-H. , Ma, E. , Sun, J. , Han, W.-Z. . A unified model for ductile-to-brittle transition in body-centered cubic metals . | Journal of Materials Science and Technology , 2023 , 141 , 193-198 . |
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Abstract ：
Titanium (Ti) is sensitive to small amount of oxygen interstitials, which has a major impact on its mechanical properties. Noticeable strengthening together with rapid decline in ductility induced by oxygen solutes poses a serious limitation for processing and application of Ti alloys. Here, we alleviate this dilemma by designing a unique oxygen-gradient in pure Ti, achieving a nontrivial combination of ultra-hardenability, high strength, toughness, and enhanced strain hardening rate. Plausible mechanism for such an oxygen-regulated plasticity in hexagonal Ti is proposed, which depends on twinning coordinating plasticity after yielding and oxygen-solute mediated dislocation slip subsequently. The dislocations glide on the common prismatic plane at low oxygen concentration, then prevail on the unusual 1st order pyramidal plane and then transfer to the peculiar basal plane and the 2nd order pyramidal plane with increasing oxygen content. These findings provide an effective mean to optimize pure Ti with desirable mechanical performance.
Keyword ：
Dislocation Hardening Oxygen solutes Slip system Titanium
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| GB/T 7714 | Wang, Xiu-Qun , Han, Wei-Zhong . Oxygen-gradient titanium with high strength, strain hardening and toughness [J]. | ACTA MATERIALIA , 2023 , 246 . |
| MLA | Wang, Xiu-Qun et al. "Oxygen-gradient titanium with high strength, strain hardening and toughness" . | ACTA MATERIALIA 246 (2023) . |
| APA | Wang, Xiu-Qun , Han, Wei-Zhong . Oxygen-gradient titanium with high strength, strain hardening and toughness . | ACTA MATERIALIA , 2023 , 246 . |
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Abstract ：
In this work, using in-situ uniaxial tensile and compressive testing, microscopy, and theoretical analysis, we study the mechanism underlying the ultrahigh irradiation hardening in niobium (Nb). We show that irradiated Nb pillar exhibits a more than two-fold increase in the yield stress. With in-situ mechanical testing, we observe that He bubbles in Nb promote dislocation nucleation and multiple slip systems. The Nb pillars with 1.2 nm He bubbles fail by bubble coalescence and form a faceted fracture surface. In contrast, the Nb pillars with 8 nm He bubbles fail by bubble elongation and fragmentation. A theoretical analysis of the hardening contribution based solely on the density and size of He bubbles finds that it is less than one third of the experimentally observed hardening. To explain the large gap between the model and the experiment, we propose that the ultrahigh irradiation hardening originates from a large quantity of atomic-size, undetectable He-vacancy (He-V) complexes. The implanted He ions only account for less than 50% percent in the visible He bubbles, while most of them bind to vacancies to form stable He-V complexes that are distributed throughout the lattice. The strong interaction between dislocations and high density of He-V complexes is the chief source for the remarkable irradiation hardening observed in Nb.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keyword ：
Complex Hardening Helium Irradiation Niobium
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| GB/T 7714 | Li, Jing-Ting , Beyerlein, Irene J. , Han, Wei-Zhong . Helium irradiation-induced ultrahigh hardening in niobium [J]. | ACTA MATERIALIA , 2022 , 226 . |
| MLA | Li, Jing-Ting et al. "Helium irradiation-induced ultrahigh hardening in niobium" . | ACTA MATERIALIA 226 (2022) . |
| APA | Li, Jing-Ting , Beyerlein, Irene J. , Han, Wei-Zhong . Helium irradiation-induced ultrahigh hardening in niobium . | ACTA MATERIALIA , 2022 , 226 . |
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Abstract ：
Titanium (Ti) is a promising biomedical material due to its superior corrosion resistance, low elastic modulus and favorable biocompatibility. Nevertheless, Ti faces a dilemma because of its inferior abrasion performance and strength-ductility trade-off, which poses a limitation in application as biomedical implants. Here, we developed an oxygen-charging method to fabricate a beta-Ti alloy with combination of ultrahigh surface hardness, strength, toughness and remarkable wear resistance. The superior mechanical performance of beta-Ti alloy originates from a 200 mu m-thick alpha+beta phase hard shell, a 600 mu m oxygen gradient region and an oxygen-free beta-Ti core. The gradient phase and composition structures display different deformation mechanisms, transforming from simple but unusual basal slip in a phase to multiple-slip activities in beta phase. The unique oxygen gradient distribution makes beta-Ti alloy much stronger and tougher that can resist surface crack propagation and sample catastrophic failure. Oxygen charging is a novel technique to design high-performance Ti implants for biomedical applications. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keyword ：
beta-Ti Hardening Oxygen-charging Toughness Wear
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| GB/T 7714 | Wang, Xiu-Qun , Zhang, Yu-Sheng , Han, Wei-Zhong . Design of high strength and wear-resistance beta-Ti alloy via oxygen-charging [J]. | ACTA MATERIALIA , 2022 , 227 . |
| MLA | Wang, Xiu-Qun et al. "Design of high strength and wear-resistance beta-Ti alloy via oxygen-charging" . | ACTA MATERIALIA 227 (2022) . |
| APA | Wang, Xiu-Qun , Zhang, Yu-Sheng , Han, Wei-Zhong . Design of high strength and wear-resistance beta-Ti alloy via oxygen-charging . | ACTA MATERIALIA , 2022 , 227 . |
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Abstract ：
Synergetic strengthening by designing of gradient nanostructures is a novel method to enhance strength in metals and alloys. Herein, we realize synergetic strengthening in strain-softening Zn alloy with gradient nanostructures. The results show that synergetic strengthening accounts for at least 25.5 pct of the yield strength of the strain-softening Zn alloy. The synergetic strengthening is induced by the microstructural gradient and the resultant strength gradient regardless of specific hardening or softening of the refined microstructures.
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| GB/T 7714 | Zhang, Wei , Du, Yan , Han, Wei-Zhong et al. Gradient Microstructure Induced Synergetic Strengthening in Strain-Softening Zn Alloy [J]. | METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE , 2021 , 53 (1) : 12-17 . |
| MLA | Zhang, Wei et al. "Gradient Microstructure Induced Synergetic Strengthening in Strain-Softening Zn Alloy" . | METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 53 . 1 (2021) : 12-17 . |
| APA | Zhang, Wei , Du, Yan , Han, Wei-Zhong , Huo, Wang-Tu , Hu, Jiang-Jiang . Gradient Microstructure Induced Synergetic Strengthening in Strain-Softening Zn Alloy . | METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE , 2021 , 53 (1) , 12-17 . |
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Abstract ：
Tungsten displays high strength in extreme temperature and radiation environments and is considered a promising plasma facing material for fusion nuclear reactors. Unlike other metals, it experiences substantial irradiation hardening, which limits service life and presents safety concerns. The origin of ultrahigh-irradiation hardening in tungsten cannot be well-explained by conventional strengthening theories. Here, we demonstrate that irradiation leads to near 3-fold increases in strength, while the usual defects that are generated only contribute less than one-third of the hardening. An analysis of the distribution of tagged atom-helium ions reveals that more than 87% of vacancies and helium atoms are unaccounted for. A large fraction of helium-vacancy complexes are frozen in the lattice due to high vacancy migration energies. Through a combination of in situ nanomechanical tests and atomistic calculations, we provide evidence that irradiation hardening mainly originates from high densities of atomic-scale hidden point-defect complexes.
Keyword ：
Dislocation Hardening Helium Irradiation Tungsten
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| GB/T 7714 | Zheng, Ruo-Yao , Jian, Wu-Rong , Beyerlein, Irene J. et al. Atomic-Scale Hidden Point-Defect Complexes Induce Ultrahigh-Irradiation Hardening in Tungsten [J]. | NANO LETTERS , 2021 , 21 (13) : 5798-5804 . |
| MLA | Zheng, Ruo-Yao et al. "Atomic-Scale Hidden Point-Defect Complexes Induce Ultrahigh-Irradiation Hardening in Tungsten" . | NANO LETTERS 21 . 13 (2021) : 5798-5804 . |
| APA | Zheng, Ruo-Yao , Jian, Wu-Rong , Beyerlein, Irene J. , Han, Wei-Zhong . Atomic-Scale Hidden Point-Defect Complexes Induce Ultrahigh-Irradiation Hardening in Tungsten . | NANO LETTERS , 2021 , 21 (13) , 5798-5804 . |
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Abstract ：
Interface engineering is a useful method to reduce the accumulation of irradiation defects in metals. Here, we study the effect of interface on the formation of dislocation loops in helium and krypton ions irradiated nanolayered Zr-2.5Nb. Nanolaminated alpha/beta-Zr duplex-phase structures remain stable after irradiation at 400 degrees C up to 20 dpa. Dislocation denuded zones with width of 30 to 40 nm are formed at interfaces. The number density and size of both a-loops and c-loops are smaller in nanolayered sample because of interface accelerating point defects recombination. These observations indicate that alpha/beta-Zr interfaces effectively reduce dislocation loops formation. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keyword ：
Dislocation loop Interface Irradiation Zr-2.5Nb
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| GB/T 7714 | Zhang, Jie-Wen , Liu, Si-Mian , Han, Wei-Zhong . Interfaces Reduce Dislocation Loop Formation in Irradiated Nanolayered Zr-2.5Nb [J]. | SCRIPTA MATERIALIA , 2021 , 200 . |
| MLA | Zhang, Jie-Wen et al. "Interfaces Reduce Dislocation Loop Formation in Irradiated Nanolayered Zr-2.5Nb" . | SCRIPTA MATERIALIA 200 (2021) . |
| APA | Zhang, Jie-Wen , Liu, Si-Mian , Han, Wei-Zhong . Interfaces Reduce Dislocation Loop Formation in Irradiated Nanolayered Zr-2.5Nb . | SCRIPTA MATERIALIA , 2021 , 200 . |
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Abstract ：
Hierarchical 3D nanolayered Zr-2.5Nb has high strength, strain hardening and ductility because of the 3D alpha/beta-Zr networks, which is a promising structural material for nuclear reactor. However, excellent thermal stability is of great importance for materials service in nuclear reactor. Here, we study thermal stability of the hierarchical 3D nanolayered Zr-2.5Nb. After 1 h annealing at various temperatures below 700 degrees C, alpha-Zr layer thickness only has a slightly increase. The hardness, yield strength and uniform elongation of the sample remain unchanged. Interface orientation relationship and layer morphology keep stable after annealing, indicating high thermal stability. The duplex phase structures coarsen quickly after annealing at 1000 degrees C. An obvious increase in hardness and yield strength was observed when sample annealed at 300 degrees C, which relates to the precipitation of omega(iso) phase in beta-Zr. Controlling the number of omega(iso) phase is likely a strategy to further enhance the strength and ductility of the alloy.
Keyword ：
5Nb Annealing Microstructure Nanolayer Strength Zr-2
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| GB/T 7714 | Zou, Xiao-Wei , Zhang, Jie-Wen , Han, Wei-Zhong . Thermal stable hierarchical 3D nanolayered Zr-2.5Nb [J]. | JOURNAL OF MATERIALS RESEARCH , 2021 , 36 (13) : 2630-2638 . |
| MLA | Zou, Xiao-Wei et al. "Thermal stable hierarchical 3D nanolayered Zr-2.5Nb" . | JOURNAL OF MATERIALS RESEARCH 36 . 13 (2021) : 2630-2638 . |
| APA | Zou, Xiao-Wei , Zhang, Jie-Wen , Han, Wei-Zhong . Thermal stable hierarchical 3D nanolayered Zr-2.5Nb . | JOURNAL OF MATERIALS RESEARCH , 2021 , 36 (13) , 2630-2638 . |
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Abstract ：
Hydride precipitates that develop in Zr after absorbing hydrogen can impart significant material hardening and embrittlement. Here, we use electrolytic hydrogen charging to synthesize Zr samples with different subsurface hydride aging times and transmission electron microscopy to understand the mechanisms underlying hydride precipitation and their distributions across the microstructure of pure Zr. Subsurface hydride formation involves volumetric swelling, causing the sample surface to produce bumps. Analysis of the morphologies and spatial distributions of these bumps can reveal several important characteristics of hydrides below. The analysis indicates that subsurface hydrides first form by isolated nucleation followed by coalescence. The shape of the hydride bump is found to be determined by the angle between the basal plane of the subsurface hydride and the sample surface. We reveal that, at room temperature, the hydride phase transition sequence follows gamma-ZrH delta-ZrH1.66 -> epsilon-ZrH2. The two main alpha-Zr/hydride orientation relationships are 1) (0001)(alpha)parallel to(11 (1) over bar)(delta) with [2 (11) over bar0](alpha)parallel to[011](delta) or 2) (0001)(alpha)parallel to(001)(gamma/delta) with [1 (2) over bar 10](alpha)parallel to[110](gamma/delta). Last, we show that the orientation of the basal plane plays a decisive role in the formation of both intragranular and intergranular subsurface hydrides. Statistical analysis of several hundred grain boundaries reveals that grain boundaries with c-axis misorientation of <15 degrees, =55 degrees-60 degrees and >85 degrees are preferential sites for subsurface hydride formation, while those with c-axis misorientations higher than 15 degrees and one grain's basal plane nearly perpendicular to the grain boundary plane resist hydride precipitation. These findings can guide grain boundary engineering efforts for controlling hydrogen damage in Zr. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keyword ：
Basal plane Grain boundary Hydride Precipitation Zirconium
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| GB/T 7714 | Jia, Yu-Jie , Beyerlein, Irene J. , Han, Wei-Zhong . Precipitation characteristics and distributions of subsurface hydrides in zirconium [J]. | ACTA MATERIALIA , 2021 , 216 . |
| MLA | Jia, Yu-Jie et al. "Precipitation characteristics and distributions of subsurface hydrides in zirconium" . | ACTA MATERIALIA 216 (2021) . |
| APA | Jia, Yu-Jie , Beyerlein, Irene J. , Han, Wei-Zhong . Precipitation characteristics and distributions of subsurface hydrides in zirconium . | ACTA MATERIALIA , 2021 , 216 . |
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Abstract ：
Body-centered cubic metals including steels and refractory metals suffer from an abrupt ductile-to-brittle transition (DBT) at a critical temperature, hampering their performance and applications. Temperature-dependent dislocation mobility and dislocation nucleation have been proposed as the potential factors responsible for the DBT. However, the origin of this sudden switch from toughness to brittleness still remains a mystery. Here, we discover that the ratio of screw dislocation velocity to edge dislocation velocity is a controlling factor responsible for the DBT. A physical model was conceived to correlate the efficiency of Frank-Read dislocation source with the relative mobility of screw versus edge dislocations. A sufficiently high relative mobility is a prerequisite for the coordinated movement of screw and edge segments to sustain dislocation multiplication. Nanoindentation experiments found that DBT in chromium requires a critical mobility ratio of 0.7, above which the dislocation sources transition from disposable to regeneratable ones. The proposed model is also supported by the experimental results of iron, tungsten, and aluminum.
Keyword ：
brittle dislocation ductile mobility
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| GB/T 7714 | Lu, Yan , Zhang, Yu-Heng , Ma, En et al. Relative mobility of screw versus edge dislocations controls the ductile-to-brittle transition in metals [J]. | PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA , 2021 , 118 (37) . |
| MLA | Lu, Yan et al. "Relative mobility of screw versus edge dislocations controls the ductile-to-brittle transition in metals" . | PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 118 . 37 (2021) . |
| APA | Lu, Yan , Zhang, Yu-Heng , Ma, En , Han, Wei-Zhong . Relative mobility of screw versus edge dislocations controls the ductile-to-brittle transition in metals . | PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA , 2021 , 118 (37) . |
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