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Influences of size and position of defects on the fatigue life of electron beam welded-aluminum alloy joints
LU Li, ZHAO Haiyan, CAI Zhipeng, CUI Xiaofang
Front. Mater. Sci.. 2007, 1 (2): 130-133.
https://doi.org/10.1007/s11706-007-0023-z
Defects such as pores influence the fatigue life of electron beam-welded aluminum alloy joints. In this paper, the influences of pore size and position on the fatigue life of aluminum overlap joint are studied. A finite element model (FEM), combined with experimental data, is established to evaluate the fatigue life of overlap joints. By employing this FE model, the effects of pore size and position on fatigue lives of overlap joints are investigated and discussed. From the present study, when pore position is closer to the weld bead tip or the faying surface, the fatigue life decreases. Also, there is a critical size for the pore; when the pore size is larger than the critical value, the fatigue strength decreases sharply.
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The structure and photoluminescence properties of ZnO/SiC multilayer film on Si substrate
JIN Chenggang, WU Xuemei, SHA Zhendong, ZHUGE Lanjian
Front. Mater. Sci.. 2007, 1 (2): 158-161.
https://doi.org/10.1007/s11706-007-0028-7
ZnO/SiC multilayer film has been fabricated on a Si (111) substrate with a silicon carbide (SiC) buffer layer using the RF (radio frequency)-magnetron technique with targets of a ceramic polycrystalline zinc oxide (ZnO) and a composite target of pure C plate with attached Si chips on the surface. The as-deposited films were annealed at a temperature range of 600 1000?C under nitrogen atmosphere. The structure and photoluminescence (PL) properties of the samples were measured using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and PL spectrophotometry. By increasing the annealing temperature to 800?C, it is found that all the ZnO peaks have the strongest intensities, and the crystallinity of ZnO is more consistent on the SiC buffer layer. Further increase of the annealing temperature allows the ZnO and SiC layers to penetrate one another, which makes the interface between ZnO and SiC layer become more and more complicated, thus reduces the crystallinities of ZnO and SiC. The PL properties of a ZnO/SiC multilayer are investigated in detail. It is discovered that the PL intensities of these bands reach their maximum after being annealed at 800?C. The PL peaks shift with an increase in the annealing temperature, which is due to the ZnO and SiC layers penetrating reciprocally. This makes the interface more impacted and complicated, which induces band structure deformation resulting from lattice deformation.
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High cycle fatigue characteristics of 2124-T851 aluminum alloy
LI Xue, YIN Zhimin, PAN Qinglin, JIANG Feng, NIE Bo, ZHONG Li
Front. Mater. Sci.. 2007, 1 (2): 168-172.
https://doi.org/10.1007/s11706-007-0030-0
The fatigue crack growth rate, fracture toughness and fatigue S-N curve of 2124-T851 aluminum alloy at high cycle fatigue condition were measured and fatigue fracture process and fractography were studied using optical microscopy (OM), X-ray diffraction (XRD) technique, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that at room temperature and R = 0.1 conditions, the characteristics of fatigue fracture could be observed. Under those conditions, the fatigue strength and the fracture toughness of a 2124-T851 thick plate is 243 MPa and 29.64 MPa · m1/2, respectively. At high cycle fatigue condition, the higher the stress amplitude, the wider the space between fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area, and the greater the ratio between the intermittent fracture area and the whole fracture area.
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Fabrication of an electronic package box of SiCP/Al composites with high volume SiCP
CHU Ke, JIA Chengchang, YIN Fazhang, MEI Xuezhen, QU Xuanhui
Front. Mater. Sci.. 2007, 1 (2): 181-186.
https://doi.org/10.1007/s11706-007-0033-x
In this paper, a SiCP preform was prepared by Powder Injection Molding (PIM), and the melting aluminum was injected into the SiCP preform by the pressure infiltration method to manufacture an electronic package box of SiCP (65%)/Al composites. SiCP (65%)/Al composite prepared by pressure infiltration has full density and a homogeneous microstructure. The relative density of the composite is higher than 99%, the thermal expansion coefficient and thermal conductivity of the composite are 8.0?10 6/K and nearly 130 W/(m °K) at room temperature, respectively, which meet the requirements of electronic packaging.
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Fabrication and characterization of hydroxyapatite microspheres obtained by ultrasonic atomization method
WANG Aijuan, LU Yupeng, CHEN Chuanzhong, SUN Ruixue
Front. Mater. Sci.. 2007, 1 (2): 210-214.
https://doi.org/10.1007/s11706-007-0037-6
Two kinds of hydroxyapatite microspheres were prepared using an ultrasonic atomization method. The surface morphology, phase composition, size distribution and specific surface area were determined by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffractometry and laser diffraction particle size analysis, respectively. The results indicate that the hydroxyapatite microspheres are composed of nanosized crystals and have porous surface morphology. The specific surface areas are different before sintering, and have a slight difference after sintering. The size distribution of the microspheres added with Lopon 885 is narrow and the average size is smaller than those fabricated without the addition of Lopon 885. Besides, the impurity phase, tetracalcium phosphate, appeared during ultrasonic atomizing procedure, and can be completely removed after sintering at 650vH for 1 h.
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Fabrication of gradient material by electron beam smelting based on scanning track control
YANG Shanglei, XUE Xiaohuai, LOU Songnian, LU Fenggui
Front. Mater. Sci.. 2007, 1 (2): 220-224.
https://doi.org/10.1007/s11706-007-0039-4
A new electron beam (EB) control system was developed in a general vacuum EB machine by equipping it with an industrial control computer, programmable logic control (PLC), deflection coil, data acquisition card, power amplifier, etc. In this control system, the scanning track and energy distribution of the EB could be edited off-line, adjusted in real-time, and controlled on-line. Ti-Mo gradient material (GM) with high temperature resistance was fabricated using electron beam smelting (EBS) control. The smelting pro cesses include three steps such as preheating, smelting, and homogenizing. The results show that GM prepared by using smelting technology has fine appearance, and has good integrated interface with Ti alloy. The Mo and Ti elements are gradual diversification in the interface of the gradient material. The microstructure near the Ti alloy base metal is α+β basket-waver grain, and the microstructure near GM is single phase of β solid solution.
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