A material in the system W/W-Cu/Cu with a density gradient, which has an important application in dynamic high pressure physics, was prepared by one-step hot-press sintering. W-Cu composite interlayers were produced f...
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ISBN:
(纸本)9788880800842
A material in the system W/W-Cu/Cu with a density gradient, which has an important application in dynamic high pressure physics, was prepared by one-step hot-press sintering. W-Cu composite interlayers were produced from W and Cu powders with Zn (2wt%) as the sintering aid. With increasing the sintering temperature, the relative density of W-Cu composites increased, reaching a higher value (>96%) at 850°C. Then by inserting three W-Cu composite interlayers between the tungsten and copper alloy plates followed by one-step hot-press at 850°C-20MPa-60min, a wholly dense W/W-Cu/Cu system functionally graded material was obtained, which had a large density range from 8.9 to 17.25g/cm3.
EVA plastic film is the keymaterial for V-process. Through decades of research, special EVA film for V-process has been produced. The film has adequate elongation; its maximum is about 800% in longitudinal direction ...
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EVA plastic film is the keymaterial for V-process. Through decades of research, special EVA film for V-process has been produced. The film has adequate elongation; its maximum is about 800% in longitudinal direction and 750% in transversal direction. The single width of the film is 2.8 m and the double width is 5.6 m, which is the widest sheet film for V-process in China. Sheets with different thickness ranging from the thickest 0.35 mm to the thinnest 0.08 mm can meet different demands in China. The film can be used not only for V-process of iron castings, but also for the manganese steel railway frog, steel rocking support and side frame castings for train and the steel bridge box for engine truck.
The preparation of semi-solid slurry of hypereutectic Al-Si alloy by Ultrasonic Vibration (USV) has been studied. The A390 alloy melt was poured into a preheated metal cup, and subsequently the ultrasonic vibrator was...
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ISBN:
(纸本)9771012039401
The preparation of semi-solid slurry of hypereutectic Al-Si alloy by Ultrasonic Vibration (USV) has been studied. The A390 alloy melt was poured into a preheated metal cup, and subsequently the ultrasonic vibrator was dipped into the melt and USV was imposed. The solidified microstructure of the slurry has been analyzed, and the mechanical properties of the alloy have been tested by making samples through diecasting of the slurry. The results show that the primary Si particles of A390 alloy became finer, rounder and uniformly distributed in microstructure of A390 alloy slurry if imposed with USV, and average diameter of primary Si particles was about 20m. With USV, the ultimate tensile strength and the hardness of rheo-casted samples increased by over 25% and near 50% respectively besides the elongation rose by above 100%. After heat treatment, the mechanical properties were further improved. In addition, the mechanism of preparation of semi-solid slurry of hypereutectic Al-Si alloy by USV is discussed.
α-Al2O3 nanopowders were prepared by a novel synthesis process, using the nanosized α-Al2O3 obtained from pyrolyzing ammonium aluminum carbonate hydroxide as seeds and the self-dispersed nanosized AlOOH crystal powd...
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α-Al2O3 nanopowders were prepared by a novel synthesis process, using the nanosized α-Al2O3 obtained from pyrolyzing ammonium aluminum carbonate hydroxide as seeds and the self-dispersed nanosized AlOOH crystal powders as precursors. Based on their good self-dispersion in water, the α-Al2O3 seeds were dispersed evenly into the AlOOH sol by the new homodispersion mixing technique. This process enables the conversion of AlOOH to alumina at 190°C (hydrothermal temperature), in which the alumina is calcined to nanosized alpha-alumina having an average length to diameter ratio of 60nm:15nm at 930°C. In the synthesis reaction for transforming the AlOOH to alumina, the effect of superfine pulverization and self-dispersion of the precursors was studied.
A novel hybrid method is proposed in the paper, which is an assistant tool for product designers to estimate springback in sheet metal forming process at the preliminary design stage. In the hybrid method, the forming...
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A novel hybrid method is proposed in the paper, which is an assistant tool for product designers to estimate springback in sheet metal forming process at the preliminary design stage. In the hybrid method, the forming results are obtained firstly by an inverse finite element approach (IA) with a membrance element. The thickness strain and stress can be calculated according to the approximate curvature radius of the discrete meshes. Then, a rotation-free shell element is employed, with only three displacements at the corner nodes of the element, to calculate the springback. To verify the accuracy and efficiency of the hybrid method, the numerical results of the hybrid method on two benchmark tests are compared with experimental results.
Potassium lithium niobate (KLN:K3Li2Nb5O15) thin films have been deposited on quartz glass by pulsed laser deposition (PLD) technique using a stoichiometric KLN target, which was prepared by solid reaction with K2CO3,...
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Potassium lithium niobate (KLN:K3Li2Nb5O15) thin films have been deposited on quartz glass by pulsed laser deposition (PLD) technique using a stoichiometric KLN target, which was prepared by solid reaction with K2CO3, Li2CO3, and Nb2O5 powders as starting materials. X-ray diffraction (XRD) and Raman studies have revealed that tetragonal tungsten-bronze-type structure of KLN films with (310) preferred orientation could be achieved at the substrate temperature of 700°C and the oxygen partial pressure of 10 Pa. The average transmittance of as-deposited thin films in the visible range was nearly 90%.
The 5-axis milling processes were conducted with several uncoated WC-Co tools, which are with taper ball end mills with four flutes. There is a severe problem of high rate of tool failure, which has led to the high co...
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The 5-axis milling processes were conducted with several uncoated WC-Co tools, which are with taper ball end mills with four flutes. There is a severe problem of high rate of tool failure, which has led to the high cost and low productivity of the milling process. In order to find out the real reason, some former work, which included the tool geometry analysis, tool path and tool posture analysis, as well as the cutting force calculating, had been done. It has been found that most of the tool failures are resulted from cutting edge chipping or the workpiece material of titanium alloys attached to the tool, Meanwhile, a suddenly applied load or an abrupt unloading of the tool at the end of a cut is another important factor. Moreover, the tool materials had been analyzed, which included the element composition analysis with XRD, the microstructure analysis with SEM. XRD results indicate the cobalt at the tip of tool is less than at the shank of tool. SEM results indicate there are micro-cracks concentrated in the cutting edge area. The tool material failure mechanism will be set up based on the tool material analysis in this study.
The high intensity of thermal stress was generated during fabrication of 6063 aluminum/60SiC‐35Al‐5Si double‐layer material. In order to decrease the thermal stress, graded materials of Al/60SiC‐35Al‐5Si was fabr...
The high intensity of thermal stress was generated during fabrication of 6063 aluminum/60SiC‐35Al‐5Si double‐layer material. In order to decrease the thermal stress, graded materials of Al/60SiC‐35Al‐5Si was fabricated by spark plasma sintering. The CTE in the graded layer was controlled by SiC fraction and particle sizes. The calculation results indicate that the net stress of more than 800 MPa was generated in the double‐layer materials, but it decreased to 170 MPa or less in the graded materials. So the stability can be guaranteed in the graded composites. The graded layers also have the potential for high thermal conductivity, more than 180W/Mk for every layer, which satisfies the application.
A study of silicon nitride ceramic radomes, which includes preparation of the material and optimal design of the radome wall structure, is presented in this paper. Multilayer radome wall structure with high dielectric...
A study of silicon nitride ceramic radomes, which includes preparation of the material and optimal design of the radome wall structure, is presented in this paper. Multilayer radome wall structure with high dielectric constant skins and a low dielectric constant core layer is used for broadband application. As a candidate material for both the skins and core layer, silicon nitride ceramics of controlled dielectric constant in the range 3.0∼7.5 were prepared by adding different content of sintering aids such as magnesia, alumina, silica and zirconium phosphate binder and choosing suitable sintering methods. A computer aided design (CAD) for the wall structure of silicon nitride multilayer ceramic radome based on microwave equivalent network method is carried out according to design requirements. By optimizing the thickness of skins and core layer, the power transmission efficiency of such a multilayer Si3N4 ceramic radome is calculated. The calculated results suggest that when the dielectric constant of skins lies in the range 6∼7.5 and core layer in the range 3.5∼4, the power transmission efficiency is above 85% with frequency of 2∼18 GHz while the thickness of skins is less than 0.03λ and the thickness ratio of skins to core layer is less than 1:15.
In the present study, Si3N4 ceramics with pore gradient structure were prepared by spark plasma sintering (SPS) technique. Silicon nitride ceramics with different controlled porosities were prepared by using ZrP2O7 as...
In the present study, Si3N4 ceramics with pore gradient structure were prepared by spark plasma sintering (SPS) technique. Silicon nitride ceramics with different controlled porosities were prepared by using ZrP2O7 as a binder material and heat treated at 1100 °C in a pressureless nitrogen atmosphere. Si3N4 ceramics with controlled porosity of 34–47% were obtained. The distribution of porous structure was homogenous. Fully dense Si3N4 ceramics could be sintered at 1400∼1600 °C by using MgO and alumina Al2O3 as the sintering aids. Pore gradient structure was formed by laminating the Si3N4 porous ceramics and powder mixture was used to obtain fully dense ceramics, and then sintering at 1400–1600 °C. Microstructure of sintered samples was observed by scanning electronic microscope (SEM) and the change of phase compositions was analyzed by X‐ray diffraction (XRD). The results showed that these samples exhibited a good porous graded structure with a highly porous layer and a dense surface layer. The major phase of the Si3N4 ceramics was still α phase.
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