Solid State Communications
Quantum coherence effect on the conductance scaling law G similar to L(-theta) of a fractal nonbranching Koch curve is addressed. The quantum conductivity exponent theta of the fractal is exactly solved by combining the Landauer formula with a renormalization decimation transformation.
关键词:
Zhihua LIU
,
Qing ZHAO
,
Deqing LI
材料科学技术（英文）
In this paper, technology margin experiment of hollow cathode fusion are welding (FAW) and penetrating are welding (PAW) is presented in detail. The advantages of PAW, compared with FAW, are better weld formation, narrower welds, as well as a larger welding technology margin. Technological experiment and hydraulic test for the Ti alloy pressure vessels with PAW are described. Also, the weld formation control on Ti alloys is preliminarily analyzed. Finally, conclusions are addressed.
关键词:
Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
Friction stir processing (FSP), developed based on the basic principles of friction stir welding (FSW), a solid-state joining process originally developed for aluminum alloys, is an emerging metalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. The FSP causes intense plastic deformation, material mixing, and thermal exposure, resulting in significant microstructural refinement, densification, and homogeneity of the processed zone. The FSP technique has been successfully used for producing the fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ. In this review article, the current state of the understanding and development of FSP is addressed.
关键词:
strain-rate superplasticity;cast nial bronze;al-mg-zr;low-temperature;superplasticity;nickel-aluminum bronze;particle-size ratio;mechanical-properties;microstructural modification;magnesium alloy;grain-refinement
NIEH Tai-Gang
,
WADSWORTH Jeffrey (Lawrence Livermore National Laboratory
,
Livermore
,
CA 94550
,
USA)
金属学报(英文版)
Superplasticity in intermetallic alloys is reviewed. Intermetallics which have been demonstrated to be superplastic include nickel-based (Ni_3Al, Ni_3Si), titanium-base (Ti_3Al, TiAl), and iron-base (Fe_3Al, FeAl) alloys. These alloys are primarily finegrained, two phase materials. But, superplasticity was also observed in some iron-base alloys which were in coarsegrained conditions. These alloys behave like Class I solid solution. The superplastic deformation mechanisms as well as microstructural characteristics are discussed. The superplastic forming of intermetallics is also briefly addressed.
关键词:
: Superplasticity
,
null
,
null
,
null
Journal of Magnetism and Magnetic Materials
Electronic structure, Born effective charges, and spontaneous polarization of multiferroic single crystal BiMn(2)O(5) have been investigated in the framework of density functional theory. The relative stability of the ground state and the origin of multiferroicity for magnetism and ferroelectricity are addressed. The results reveal that the stability of antiferromagnetic (AFM) state is better than the ferromagnetic (FM) and ferrimagnetic configurations. The Born effective charge tensors (Z*) have been calculated for this compound using a Berry-phase approach, compared to their nominal ionic values, the Z* of Mn atoms show anomalous difference. By investigating the electric structure of BiMn(2)O(5), there exists obviously hybridization between Bi 6s and O 2p states, our calculations indicate that the 6s(2) lone pair on the formally trivalent Bi ion plays an important role in inducing the ferroelectric distortion. (C) 2011 Elsevier B.V. All rights reserved.
关键词:
First principles;Born effective charge;Electronic structure;Berry-phase method;electric polarization;manganites;charge
Carbon
It is predicted theoretically and understood experimentally that carbon nanotubes (CNTs) possess excellent physical and chemical properties and have wide-range potential applications. However, only some of these properties and applications have been verified or realized. To a great extent, this situation can be ascribed to the difficulties in getting high-purity CNTs. Because as-prepared CNTs are usually accompanied by carbonaceous or metallic impurities, purification is an essential issue to be addressed. Considerable progress in the purification of CNTs has been made and a number of purification methods including chemical oxidation, physical separation, and combinations of chemical and physical techniques have been developed for obtaining CNTs with desired purity. Here we present an up-to-date overview on the purification of CNTs with focus on the principles, the advantages and limitations of different processes. The effects of purification on the structure of CNTs are discussed, and finally the main challenges and developing trends on this subject are considered. This review aims to provide guidance and to stimulate innovative thoughts on the purification of CNTs. (C) 2008 Elsevier Ltd. All rights reserved.
关键词:
chemical-vapor-deposition;scanning probe microscopy;field-flow;fractionation;large-scale purification;single-walled nanotubes;high-yield purification;heat-treatment;assisted purification;microwave digestion;arc-discharge
