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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ey
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A.Verma
材料科学技术（英文）
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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Zhenfang LIAO
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Shijin ZHANG
材料科学技术（英文）
Electro-hydraulic impulse water-air mixing jet by which the quality of metal materials can be improved is described in this paper. The experimental results proved that the hardness and the micro-hardness of the surface layer of metal materials can be improved with this method, for example, the microhardness of CrWMn can be increased by 35.62 percent.
关键词:
Electro-hydraulic impulse
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null
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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
Chinese Physics Letters
A focused gallium ion (Ga+) beam is used to fabricate micro/submicron spacing gratings on the surface of porous NiTi shape memory alloy (SMA). The crossing type of gratings with double-frequency (2500 l/mm and 5000 l/mm) using the focused ion beam (FIB) milling are successfully produced in a combination mode or superposition mode. Based on the double-frequency gratings, high-quality scanning electron microscopy (SEM) Moire patterns are obtained to study the micro-scale deformation of porous NiTi SMA. The grating fabrication technique is discussed in detail. The experimental results verify the feasibility of fabricating high frequency grating on metal surface using FIB milling.
关键词:
Shijian YUAN
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Gang LIU
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Xianwei TIAN
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Z.R.WANG
材料科学技术（英文）
In order to reduce high calibration pressure in hydroforming of components with too small radii, a method was proposed to manufacture automotive hollow components with rectangular shape by relatively lower pressure. The process is simulated and analyzed. It is thought that the friction force between the die surface and tube is a main reason that high pressure is needed to form small radii. Using the method proposed in this paper, a petal-like section shape is first preformed so that the central zones of the four sides of the preform section do not contact with the die sides, thus the tube metal is easy to flow into the transition radii area in calibration stage. Moreover, a positive force along the sides is produced by the internal pressure, which is beneficial to overcome the friction force and push the material into the radii. Therefore, the pressure for forming the transition radii is greatly reduced and the components with small radii can be formed with relatively lower pressure. For the experimental case conducted in this paper, the forming pressure is reduced by about 28.6% than the estimated forming pressure.
关键词:
Hydroforming
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null
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null
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Z.W. Han
金属学报(英文版)
Cold roll forming is a complicated metal processing, and it is very difficult to simulate the forming process. Based on the Updated-Lagrange method in the deformation mechanics, an elastic-plastic large deformation spline finite strip method is developed to analyze cold roll forming of a thin channel section. The longitudinal membrane strain values on the edge of the deformed strip for four one-pass sequences in different fold angles are got. Simulated results are compared with the results from previously conducted experiments. The deviation of the simulated peak strain values is within 30%compared with the experimental results.
关键词:
computer aided analysis
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null
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null
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J.Q.ZHANGD.J.YOUNG
中国腐蚀与防护学报
Metaldusting attacks iron, low and high alloy steels and nickel-or cobalt-base alloys by disintegrating bulk metals and alloys into metal particles in a coke deposit. It occurs in strongly carburising gas atmospheres (carbon activity aC>1) at elevated temperatures (400 ℃~1000 ℃). This phenomenon has been studied for decades, but the detailed mechanism is still not well understood. Current methods of protection against metal dusting are either directed to the process conditions-temperature and gas composition-or to the development of a dense adherent oxide layer on the surface of the alloy by selective oxidation. However, metal dusting still occurs by carbon dissolving in the base metal via defects in the oxide scale. The research work at UNSW is aimed at determining the detailed mechanism of metal dusting of both ferritic and austenitic alloys, in particular the microprocesses of graphite deposition, nanoparticle formation and underlying metal destruction. This work was carried out using surface observation, cross-section analysis by focused ion beam and electron microscopic examination of coke deposits at different stages of the reaction. It was found that surface orientation affected carbon deposition and metal dusting at the initial stage of the reaction. Metal dusting occurred only when graphite grew into the metal interior where the volume expansion is responsible for metal disintegration and dusting. It was also found that the metal dusting process could be significantly changed by alterations in alloy chemistry. Germanium was found to affect the iron dusting process by destabilising Fe3C but increasing the rate of carbon deposition and dusting, which questions the role of cementite in ferritic alloy dusting. Whilst adding copper to iron did not change the carburisation kinetics, cementite formation and coke morphology, copper alloying reduced nickel and nickel-base alloy dusting rates significantly. Application of these fundamental results to the dusting behaviour of engineering alloys is discussed.
关键词:
metal dusting
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