Andrej Atrens
材料科学技术（英）
Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.
关键词:
Stress corrosion cracking
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Materials Science & Engineering C-Biomimetic Materials Sensors and Systems
Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.
关键词:
bamboo;bast fiber;biomimetics;engineering composites
Science
Strengthening materials traditionally involves the controlled creation of internal defects and boundaries so as to obstruct dislocation motion. Such strategies invariably compromise ductility, the ability of the material to deform, stretch, or change shape permanently without breaking. Here, we outline an approach to optimize strength and ductility by identifying three essential structural characteristics for boundaries: coherency with surrounding matrix, thermal and mechanical stability, and smallest feature size finer than 100 nanometers. We assess current understanding of strengthening and propose a methodology for engineering coherent, nanoscale internal boundaries, specifically those involving nanoscale twin boundaries. Additionally, we discuss perspectives on strengthening and preserving ductility, along with potential applications for improving failure tolerance, electrical conductivity, and resistance to electromigration.
关键词:
strain-rate sensitivity;stacking-fault energy;nano-scale twins;cu-al;alloys;nanocrystalline metals;mechanical-properties;activation;volume;copper;deformation;behavior
Journal of Applied Physics
The alloying effect of 3d transition metal elements on the lattice constants and their site preferences in gamma'-Co(3)(Al, W) are systematically studied based on a supercell model. The lattice constant of the gamma' phase is modified by the addition of 3d transition metal elements, and it increases in the order of Fe < Ni < Mn < Cr < V < Ti. Four types of site preference are identified for these 3d elements in gamma' phase by analyzing the binding energy and the impurity formation energy. Ni, Fe, V, and Ti are recognized to stabilize the gamma' phase. Their distinct alloying effect is further revealed by investigating the impurity-induced charge density difference and the partial density of states. These results are in agreement with the experimental data ever reported. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3319650]
关键词:
augmented-wave method;co-base superalloy;electronic-structure;site;preference;ni3al;phase;temperature;stability;magnetism;alloys
Transactions of Nonferrous Metals Society of China
A simplified model was proposed targeting at the isotropic high porosity metal materials with well-distributed structure. From the model the mathematical relationship between elongation and porosity was deduced for those materials, and the relationship formula was derived generally for actual high porosity metals at last, whose validity is supported by the representative experiment on a nickel foam prepared by electrodeposition.
关键词:
high porosity metal material;elongation;porosity
Science in China Series E-Technological Sciences
A geometrical model has been established based on the structure feature of high porosity metal materials, the mathematical relationship between electrical resistivity and porosity for high porosity materials with even structure has then been deduced conveniently, and the formula for calculating the electrical resistivity of high porosity materials through porosity, which is easy to know, has been acquired further. Besides, the theoretical formula was verified to coincide with the test results well by the application taking nickel foam as an example.
关键词:
high porosity material;electrical resistivity;calculation formula;deduction;foams
P.Verma
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O.P.P
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A.Verma
材料科学技术（英）
In the present work investigations have been made to see the role of metal oxides on the performance of the silver metal oxides electrical contact materials. Silver metal oxide materials of three different compositions Ag-10CdO, Ag-7.6SnO2-2.3In2O3 and Ag-10ZnO were prepared by internal oxidation process under identical processing conditions. These materials were tested for electrical conductivity, hardness, and erosion loss. Performing an accelerated test on the actual contactor assessed the electrical performance, involving erosion loss and temperature rise of the processed materials. The arc-eroded surface was characterized under scanning electron microscope. The study of the eroded surfaces of contacts indicates that the thermal stability of metal oxides depends on nature of silver-metal oxide interface and their mode of erosion. An attempt is made to correlate the surface features of the eroded contacts with the thermal stability of metal oxides.
关键词:
Contact material
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Nano Research
Two-dimensional (2-D) layered metal-organic coordination (lead methacrylate (LDMA)) networks have been prepared in aqueous solution under mild conditions and their structure determined by single crystal diffraction. As the ligand used in our experiments is easily polymerized, these metal-organic coordination layers are therefore employed as precursors to fabricate cross-linked polymer layered materials through.-irradiated polymerization. The stabilities of the samples are significantly improved after.-irradiation. To our knowledge, this is the first time that covalent bonded polymer layered structures have been fabricated without the assistance of added surfactant or template. Such layered polymer materials cannot only act as alternatives to layered inorganic materials in some caustic environments, but also allow the generation of PbS nanoparticles (NPs) without aggregation in the polymer matrix. By exposing the polymer layer to H(2)S gas at room temperature, uniform PbS nanoparticles with an average size of about 6 nm are generated in situ. In addition, the resulting PbS NPs exhibit near-infrared (NIR) luminescent properties, which suggests the composite materials may be useful as active optical elements at communication wavelengths from 1300 to 1550 nm.
关键词:
PbS nanoparticles;layered material;near-infrared;gamma-irradiated;polymerization;in situ
