HE Jianhong TANG Xiangyun CHEN Nanping Tsinghua University
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Beijing
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China Professor
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Division of Metallic Meterials
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Department of Materials Science and Engineering
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Tsinghua University
,
Beijing
,
China
金属学报(英文版)
The permeation curves of hydrogen in ferritic-austenitic duplex stainless steel have been electrochemically determined.The apparent diffusivity of hydrogen depends on the austenite content(f_γ)at room temperature,D=(0.27+0.9/f_γ~2)(10~(-10)cm~2/s).It is simply verified that hydrogen in ferritic-austenitic duplex stainless steel diffuses in “series-connection” form through both ferrite grain and austenite grain.The apparent diffusivity is D=D_αD_γ/(f_α~2D_γ+f_γ~2D_α),where D_α,D_γ are diffusivity of hydrogen in ferrite grain and austenite grain respectively,f_α,f_γ are volume fraction,in turn,of ferrite grain and austenite grain.
关键词:
hydrogen
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null
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null
International Journal of Plasticity
The effect of sample size on the shear deformation and compressive plasticity of different metallic glasses were investigated. The experimental results showed that the deformation and fracture behaviors of samples prepared from chemically identical Zr-, Ti-, Fe-, or Mg-based metallic glass ingots were strongly dependent on the sample size and machine stiffness, and a super-high compressive plasticity was achieved in the Zr-based metallic glasses with sample size of 1.0 mm in width. It is also found that the sample size can significantly influence the density of elastic energy dissipated in the shear band: with sample size decreasing and machine stiffness increasing, the density of the elastic energy dissipated in the shear band of metallic glasses is prominently decreased, thus the shear deformation turns to be more stable, resulting in the improvement of plasticity in ductile metallic glasses and the transition from fragmentation fracture to shear fracture in brittle metallic glasses. This finding is important for the potential applications of the present metallic glasses and for designing new metallic glasses with better mechanical properties. (C) 2010 Elsevier Ltd. All rights reserved.
关键词:
Metallic glass;Size effect;Elastic energy density;Mechanical;properties;cryogenic temperatures;intrinsic plasticity;superhigh strength;tensile ductility;amorphous-alloys;forming ability;fracture;size;deformation;band
Nature Materials
Metallic glasses have a very high strength, hardness and elastic limit. However, they rarely show tensile ductility at room temperature and are considered quasi-brittle materials(1,2). Although these amorphous metals are capable of shear flow, severe plastic instability sets in at the onset of plastic deformation, which seems to be exclusively localized in extremely narrow shear bands similar to 10nm in thickness(3-13). Using in situ tensile tests in a transmission electron microscope, we demonstrate radically different deformation behaviour for monolithic metallic-glass samples with dimensions of the order of 100 nm. Large tensile ductility in the range of 23-45% was observed, including significant uniform elongation and extensive necking or stable growth of the shear offset. This large plasticity in small-volume metallic-glass samples did not result from the branching/deflection of shear bands or nanocrystallization. These observations suggest that metallic glasses can plastically deform in a manner similar to their crystalline counterparts, via homogeneous and inhomogeneous flow without catastrophic failure. The sample-size effect discovered has implications for the application of metallic glasses in thin films and micro-devices, as well as for understanding the fundamental mechanical response of amorphous metals.
关键词:
mechanical-properties;fracture-behavior;amorphous-alloys;room-temperature;shear bands;deformation;flow;plasticity;strength
Journal of Physics-Condensed Matter
The reverse Monte Carlo method was used to obtain three-dimensional discrete distributions of constitutional atoms in melt-spun CuZr and CuZrTi metallic glasses from neutron and x-ray diffraction data. It was found that the icosahedral short-range order is less stable in the CuZr binary alloy than in the Ti-doped ternary alloy. The present investigation also provides evidence on the medium-range order, characterized by some nanoscale clusters of defects, in the metallic-glassy state.
关键词:
range order;alloys;liquid
Physical Review Letters
Bulk metallic glasses are brittle and fail with no plastic strain at room temperature once shear bands propagate. How do metallic glasses deform when the size is less than that of shear bands? Here we show that Al(90)Fe(5)Ce(5) metallic glass with a size <20 nm can be extremely elongated to similar to 200%. Remarkably, even an atomic chain was formed after sample necking, which was never observed in metallic glasses. The unexpected ductility may originate from the fast surface diffusion and the absence of shear band formation, and may guide the development of ductile metallic glasses for engineering applications.
关键词:
mechanical-properties;amorphous-alloys;fracture mechanisms;matrix;composites;tensile ductility;damage;deformation
Ming CHENG
材料科学技术（英文）
A finite element analysis (FEA) model has been developed to analyze microimprinting of bulk metallic glasses (BMG) near the glass transition temperature (Tg). The results reveal an approximately universal imprinting response for BMG, independent of surface feature length scale. The scale-independent nature of BMG imprinting derives from the flow characteristics of BMG in the temperature range above Tg. It also shows that the lubrication condition has a mild influence on BMG imprinting in the temperature range above Tg.
关键词:
Bulk metallic glasses
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metallic
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glasses
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Finite
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element
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ana
Applied Physics Letters
The authors find that metallic glass can be controlled to create regularly arrayed fine multiple shear bands under small punch test, indicating that metallic glass essentially has a good plastic deformation ability and thus high ductility under suitable loading condition. The current findings imply that the initiation and propagation of shear bands in metallic glass strongly depends on the stress state and the small punch test can also be regarded as an effective method to characterize the shear deformation ability and distinguish ductile-brittle transition of different metallic glasses. (C) 2007 American Institute of Physics.
关键词:
small punch test;fracture-behavior;aspect ratio;deformation;composites;pressure;flow
