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学者姓名：单智伟
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Abstract ：
Nanoindentation on crystalline materials is generally believed to generate a three-dimensional plastic zone, which has a semi-spherical shape with a diameter no larger than a few times the indentation depth. Here, by observing nanoindentation on aluminum in situ inside a transmission electron microscope, we demonstrate that three-dimensional plasticity dominated by regular dislocations triumph as the contact size upon yielding increases above -100 nm. However, when the contact diameter is less than -50 nm, a narrow and long (hereafter referred to as "one dimensional") plastic zone can be created in front of the tip, as the indenter successively injects prismatic dislocation loops/helices into the crystal. Interestingly, this one-dimensional plastic zone can penetrate up to 150 times the indentation depth, far beyond the prediction given by the Nix-Gao model. Our findings shed new light on understanding the dislocation behavior during nanoscale contact. The experimental method also provides a potentially novel way to interrogate loop-defect interactions, and to create periodic loop arrays at precise positions for the modification of properties ( e.g. , strengthening). (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keyword ：
Dislocation structure Incipient plasticity Indentation size effect In situ TEM Nanoindentation
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| GB/T 7714 | Nie, Zhi-Yu , Sato, Yuji , Ogata, Shigenobu et al. Ultralong one-dimensional plastic zone created in aluminum underneath a nanoscale indent [J]. | ACTA MATERIALIA , 2022 , 232 . |
| MLA | Nie, Zhi-Yu et al. "Ultralong one-dimensional plastic zone created in aluminum underneath a nanoscale indent" . | ACTA MATERIALIA 232 (2022) . |
| APA | Nie, Zhi-Yu , Sato, Yuji , Ogata, Shigenobu , Duarte, Maria Jazmin , Dehm, Gerhard , Li, Ju et al. Ultralong one-dimensional plastic zone created in aluminum underneath a nanoscale indent . | ACTA MATERIALIA , 2022 , 232 . |
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Abstract ：
The size of abrasive particle has a great impact on the fundamental friction behavior and mechanical properties of the abrasive during ultra-precision polishing performance. Here, the size effect of the tribological behavior and mechanical properties of CeO2 single abrasive were studied. Experimental results show that the size effect plays a role on coefficient of friction (COF) of each regime in single-asperity sliding friction, especially in ploughing and cutting regimes. The residual depth of the scratch and COF both decrease with the increase of the CeO2 tip radius. These results relate to the mechanical properties of CeO2 nanoparticles. We found that the effective modulus increases with the decrease of abrasive size, which corresponds to the size effect of the single-asperity sliding friction experiment. [GRAPHICS] .
Keyword ：
CeO2 Coefficient of friction (COF) Single asperity friction Size effect
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| GB/T 7714 | Xu, Ning , Ma, Jiahui , Liu, Qi et al. Size Effect of CeO2 Particle on Nanoscale Single-Asperity Sliding Friction [J]. | TRIBOLOGY LETTERS , 2022 , 70 (1) . |
| MLA | Xu, Ning et al. "Size Effect of CeO2 Particle on Nanoscale Single-Asperity Sliding Friction" . | TRIBOLOGY LETTERS 70 . 1 (2022) . |
| APA | Xu, Ning , Ma, Jiahui , Liu, Qi , Han, Weizhong , Shan, Zhiwei . Size Effect of CeO2 Particle on Nanoscale Single-Asperity Sliding Friction . | TRIBOLOGY LETTERS , 2022 , 70 (1) . |
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Abstract ：
Translational and rotational motion of solid matter is normally driven by external physical forces. Here we report that under oxygen atmosphere inside an environmental transmission electron microscope, catalytic palladium nanoparticles underwent a self-propelled, peristalsis-like locomotion on a supporting substrate at a relatively low temperature. Surprisingly, the particles maintained crystalline interior and even conserved their initial crystal orientations during the dramatic liquid-like motion. Such "peristaltic" crystal migration with shape oscillation is found to be mediated by profuse surface diffusion, under chemical driving forces from palladium-catalyzed gaseous oxidation of a carbonaceous layer. These findings open a new avenue of efficient heterogeneous catalysis, and reveal emergent behavior that can arise out of an energy-metabolizing nano-system. (C) 2021 Elsevier Ltd. All rights reserved.
Keyword ：
Carbon removal Environmental transmission electron microscopy Heterogeneous catalysis Metallic nanoparticles Peristaltic locomotion Surface diffusion
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| GB/T 7714 | Lu, Peng-Han , Xie, De-Gang , Liu, Bo-Yu et al. Peristalsis-like migration of carbon-metabolizing catalytic nanoparticles [J]. | EXTREME MECHANICS LETTERS , 2021 , 49 . |
| MLA | Lu, Peng-Han et al. "Peristalsis-like migration of carbon-metabolizing catalytic nanoparticles" . | EXTREME MECHANICS LETTERS 49 (2021) . |
| APA | Lu, Peng-Han , Xie, De-Gang , Liu, Bo-Yu , Ai, Fei , Zhang, Zhao-Rui , Jin, Ming-Shang et al. Peristalsis-like migration of carbon-metabolizing catalytic nanoparticles . | EXTREME MECHANICS LETTERS , 2021 , 49 . |
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Abstract ：
The carbon nanotube (CNT) is a compelling and promising material for industrial applications requiring high strength and rigidity. For a multi-walled CNT (MWCNT), the nominal tensile strength and Young's modulus (considering the whole cross-sectional area of the specimen) are key mechanical factors for the practical application of macroscopic fibers and composites. However, the nominal tensile strength and Young's modulus of MWCNTs are much lower than their effective tensile strength and Young's modulus (considering the fracture cross-sectional area) because the outermost graphite layer always fractures first due to the low cross-link between graphite layers. In this paper, we fabricated the carbon nanofibers (CNFs) by epitaxial growth on super-aligned MWCNT film template and conducted in situ uniaxial tensile tests on individual carbon-nanotube-templated CNFs. The individual CNFs show improved nominal mechanical performance than previously reported MWCNTs. The nominal mechanical properties enhancement of the CNFs is attributed to the effective control on load transfer between interwalls. © 2021 Author(s).
Keyword ：
Carbon nanofibers Elastic moduli Graphite Multiwalled carbon nanotubes (MWCN) Nanotubes Tensile strength Tensile testing
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| GB/T 7714 | Zhao, Wei , Zhang, Yongqiang , Wang, Xiaoguang et al. Carbon-nanotube-templated carbon nanofibers with improved mechanical performance [J]. | Journal of Applied Physics , 2021 , 129 (4) . |
| MLA | Zhao, Wei et al. "Carbon-nanotube-templated carbon nanofibers with improved mechanical performance" . | Journal of Applied Physics 129 . 4 (2021) . |
| APA | Zhao, Wei , Zhang, Yongqiang , Wang, Xiaoguang , Lu, Huanhuan , Liu, Guozhu , Wei, Jinghe et al. Carbon-nanotube-templated carbon nanofibers with improved mechanical performance . | Journal of Applied Physics , 2021 , 129 (4) . |
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Abstract ：
Vanadium dioxide (VO2) has emerged as a promising micro-actuator material for its large amplitude and high work density across the transition between the insulating (M1 and M2) and metallic (R) phase. Even though M2-R transition offers about 70% higher transformation stress than M1-R structural phase transition, the application of the M2 phase in the micro-actuators is hindered by the fact that previously, M2 phase can only stay stable under tensile stress. In this work, we propose and verify that by synthesizing the VO2 nanowires under optimized oxygen-rich conditions, stoichiometry change can be introduced into the nanowires (NWs) which in turn yield a large number free-standing single-crystalline M2-phase NWs stable at room temperature. In addition, we demonstrate that the output stress of the M2-phase NWs is about 65% higher than that of the M1-phase NWs during their transition to R phase, quite close to the theoretical prediction. Our findings open new avenues towards enhancing the performance of VO2-based actuators by using M2-R transition.
Keyword ：
martensitic transformation metal-insulator transition micro-actuator room-temperature M2 phase single crystalline vanadium dioxide (VO2) nanowires transformation strain
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| GB/T 7714 | Zhang, Yong-Qiang , Chen, Kai , Shen, Hao et al. Achieving room-temperature M-2-phase VO2 nanowires for superior thermal actuation [J]. | NANO RESEARCH , 2021 , 14 (11) : 4146-4153 . |
| MLA | Zhang, Yong-Qiang et al. "Achieving room-temperature M-2-phase VO2 nanowires for superior thermal actuation" . | NANO RESEARCH 14 . 11 (2021) : 4146-4153 . |
| APA | Zhang, Yong-Qiang , Chen, Kai , Shen, Hao , Wang, Yue-Cun , Hedhili, Mohamed Nejib , Zhang, Xixiang et al. Achieving room-temperature M-2-phase VO2 nanowires for superior thermal actuation . | NANO RESEARCH , 2021 , 14 (11) , 4146-4153 . |
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Abstract ：
Accurate control and measurement of real-time sample temperature are critical for the understanding and interpretation of the experimental results from in situ heating experiments inside environmental transmission electron microscope (ETEM). However, quantifying the real-time sample temperature remains a challenging task for commercial in situ TEM heating devices, especially under gas conditions. In this work, we developed a home-made micro-electrical-mechanical-system (MEMS) heater with unprecedented small temperature gradient and thermal drift, which not only enables the temperature evolution caused by gas injection to be measured in real-time but also makes the key heat dissipation path easier to model to theoretically understand and predict the temperature decrease. A new parameter termed as "gas cooling ability (H)", determined purely by the physical properties of the gas, can be used to compare and predict the gas-induced temperature decrease by different gases. Our findings can act as a reference for predicting the real temperature for in situ heating experiments without closed-loop temperature sensing capabilities in the gas environment, as well as all gas-related heating systems.
Keyword ：
environmental TEM (ETEM) gas cooling effect in situ heating MEMS heater temperature measurement
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| GB/T 7714 | Li, Meng , Xie, De-Gang , Zhang, Xi-Xiang et al. Quantifying Real-Time Sample Temperature Under the Gas Environment in the Transmission Electron Microscope Using a Novel MEMS Heater [J]. | MICROSCOPY AND MICROANALYSIS , 2021 , 27 (4) : 758-766 . |
| MLA | Li, Meng et al. "Quantifying Real-Time Sample Temperature Under the Gas Environment in the Transmission Electron Microscope Using a Novel MEMS Heater" . | MICROSCOPY AND MICROANALYSIS 27 . 4 (2021) : 758-766 . |
| APA | Li, Meng , Xie, De-Gang , Zhang, Xi-Xiang , Yang, Judith C. , Shan, Zhi-Wei . Quantifying Real-Time Sample Temperature Under the Gas Environment in the Transmission Electron Microscope Using a Novel MEMS Heater . | MICROSCOPY AND MICROANALYSIS , 2021 , 27 (4) , 758-766 . |
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Abstract ：
Submicrometre-sized amorphous silicon samples show an unusually large tensile strength relative to the compressive strength, which is due to the reduced shear modulus and the activation energy barrier for shear transformations under compression. Hard and brittle materials usually exhibit a much lower strength when loaded in tension than in compression. However, this common-sense behaviour may not be intrinsic to these materials, but arises from their higher flaw sensitivity to tensile loading. Here, we demonstrate a reversed and unusually pronounced tension-compression asymmetry (tensile strength exceeds compressive strength by a large margin) in submicrometre-sized samples of isotropic amorphous silicon. The abnormal asymmetry in the yield strength and anelasticity originates from the reduction in shear modulus and the densification of the shear-activated configuration under compression, altering the magnitude of the activation energy barrier for elementary shear events in amorphous Si. In situ coupled electrical tests corroborate that compressive strains indeed cause increased atomic coordination (metallization) by transforming some local structures from sp(3)-bonded semiconducting motifs to more metallic-like sites, lending credence to the mechanism we propose. This finding opens up an unexplored regime of intrinsic tension-compression asymmetry in materials.
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| GB/T 7714 | Wang, Yuecun , Ding, Jun , Fan, Zhao et al. Tension-compression asymmetry in amorphous silicon [J]. | NATURE MATERIALS , 2021 , 20 (10) : 1371-+ . |
| MLA | Wang, Yuecun et al. "Tension-compression asymmetry in amorphous silicon" . | NATURE MATERIALS 20 . 10 (2021) : 1371-+ . |
| APA | Wang, Yuecun , Ding, Jun , Fan, Zhao , Tian, Lin , Li, Meng , Lu, Huanhuan et al. Tension-compression asymmetry in amorphous silicon . | NATURE MATERIALS , 2021 , 20 (10) , 1371-+ . |
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Abstract ：
By in situ bending tests inside an environmental transmission electron microscope, we found that from the precrack tip of single crystalline aluminium cantilevers, dislocations are emitted and self-organized to build a low angle grain boundary (LAGB), along which the crack propagates more easily in hydrogen atmosphere than in vacuum. Atomistic modelling suggests that the LAGB formed can strongly trap hydrogen atoms, and its cohesive strength can be substantially reduced. These results imply that the hydrogen-induced transgranular crack in a polycrystalline metal can proceed by repeating a process of dynamically forming a hydrogenated LAGB and its subsequent separation in grain.
Keyword ：
A Aluminium B C Hydrogen embrittlement In situ bending test Low angle grain boundary Modelling studies TEM Transgranular cracking
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| GB/T 7714 | Xie, De-Gang , Wan, Liang , Shan, Zhi-Wei . Hydrogen enhanced cracking via dynamic formation of grain boundary inside aluminium crystal [J]. | CORROSION SCIENCE , 2021 , 183 . |
| MLA | Xie, De-Gang et al. "Hydrogen enhanced cracking via dynamic formation of grain boundary inside aluminium crystal" . | CORROSION SCIENCE 183 (2021) . |
| APA | Xie, De-Gang , Wan, Liang , Shan, Zhi-Wei . Hydrogen enhanced cracking via dynamic formation of grain boundary inside aluminium crystal . | CORROSION SCIENCE , 2021 , 183 . |
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Abstract ：
The deformation mechanisms in a beta-Ti reinforced Zr-based bulk metallic glass composite (BMGC) are studied by extracting submicron sized tensile coupons of the crystalline and amorphous phase in their monolithic and bilaminate composite forms and tensile testing them inside a TEM. Results show that the monolithic BCC crystalline phase and amorphous phase have high yield strains, owing to small length scale effects, but undergo negligible post-yield elongation before failure. However, the ductility of the bilaminate composite is significantly higher (similar to 12.4%), provided the thickness of its amorphous portion is < 100 nm. Real time videos, which are supplemented by molecular dynamics simulations, show that the negligible post yield elongation of the monolithic BCC crystalline phase is caused by planar slip on one of the {110} planes. However, the bilaminate composite form exhibits strain hardening, despite the occurrence of planar slip, as dislocations pile up at the impervious amorphous/crystalline interface, which in turn, activates slip on other {110} planes. Strain hardening in the crystalline phase ceases when a shear band nucleated in the amorphous phase penetrates the dendrite along one of the slip planes. These mechanisms are extended to explain the flow behavior of beta-Ti reinforced BMGCs and strategies to improve the ductility are discussed.
Keyword ：
Amorphous alloys bcc crystals Composite Dislocations In situ mechanical testing Plasticity
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| GB/T 7714 | Tian, Lin , Narayan, R. Lakshmi , Zhou, Kun et al. A real-time TEM study of the deformation mechanisms in beta-Ti reinforced bulk metallic glass composites [J]. | MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING , 2021 , 818 . |
| MLA | Tian, Lin et al. "A real-time TEM study of the deformation mechanisms in beta-Ti reinforced bulk metallic glass composites" . | MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 818 (2021) . |
| APA | Tian, Lin , Narayan, R. Lakshmi , Zhou, Kun , Babicheva, Rita , Ramamurty, Upadrasta , Shan, Zhi-wei . A real-time TEM study of the deformation mechanisms in beta-Ti reinforced bulk metallic glass composites . | MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING , 2021 , 818 . |
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Abstract ：
Taking advantage of the magnetic field inside transmission electron microscope (TEM), a unique Lorentz-force-actuated method for quantitative friction tests was developed via a commercial electromechanical holder. With this approach, a submicron-sized silver asperity sliding on a tungsten flat punch was actuated by Lorentz force due to electrical current through the punch, with the normal force imposed by the built-in transducer of the holder. The friction force was determined by tracking the elastic deflection of the fabricated cantilever from in situ video. Through correlating the friction behavior with the microstructural evolution near the silver-tungsten interface, we revealed that even when the relative motion commenced with the plastic deformation of the silver asperity, the interface can still sustain the further increasing static friction force. Exactly following the arrival of the maximum static friction force, the sliding occurred at the interface, indicating the transition from static to dynamic friction. This work enriches our understanding of the underlying physics of the dynamic friction process for metallic friction behavior. © 2021
Keyword ：
Lorentz force Silver Stiction Transmission electron microscopy Tungsten
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| GB/T 7714 | Lu, Huanhuan , Wang, Zhangjie , Yun, Di et al. A new approach of using Lorentz force to study single-asperity friction inside TEM [J]. | Journal of Materials Science and Technology , 2021 , 84 : 43-48 . |
| MLA | Lu, Huanhuan et al. "A new approach of using Lorentz force to study single-asperity friction inside TEM" . | Journal of Materials Science and Technology 84 (2021) : 43-48 . |
| APA | Lu, Huanhuan , Wang, Zhangjie , Yun, Di , Li, Ju , Shan, Zhiwei . A new approach of using Lorentz force to study single-asperity friction inside TEM . | Journal of Materials Science and Technology , 2021 , 84 , 43-48 . |
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