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71.
A. R. Khodabandeh M. Jahazi S. Yue S. T. Aghdashi 《Materials and Manufacturing Processes》2006,21(1):105-110
The influences of various reheating and forging temperatures as well as cooling rates on the microstructure and mechanical properties, particularly impact energy, during the forging of a Nb-V microalloyed steel to be used for automotive safety parts were investigated. Increasing the prior austenite grain size increased the volume percent of acicular ferrite and reduced pearlite content in the microstructure even for very low post-forging cooling rates, resulting in improved toughness and tensile strength values. Increasing the cooling rate enhanced the acicular ferrite content, thereby increasing the impact energy properties. At lower reheating temperatures the yield strength and impact energy levels are determined by the percentage of pearlite present in the microstructure; while as the cooling rate is increased the amount of acicular ferrite and retained austenite are increased, improving the toughness and tensile strength of the forged part. This effect is more pronounced for the parts solutionized at 1250°C and is related to the presence of very fine carbonitride precipitates under these conditions, which contributes to improved yield strength, particularly at higher cooling rates. An optimized forging process was determined and adapted to a 25 MN production forging press to validate the experimental results on semi-industrial production scale. By adequate control of the above parameters, high-strength, high-toughness parts (T.S. = 800 MPa, CVN = 35 J) were forged and optimum mechanical properties were achieved without the need for any additional heat treatment. 相似文献
72.
《Materials Research Bulletin》2006,41(2):376-386
The utilization of single-source molecular precursor approach to obtain II–VI and IV–VI semiconductors encapsulated in porous Vycor glass (PVG) is described. The procedure is based on the impregnation of cadmium and lead(II) diethyl-dithiocarbamate complexes, Cd(S2CNEt2)2 and Pb(S2CNEt2)2, inside the porous environment of PVG followed by a thermal treatment of the glass. The pyrolysis of the impregnated precursor gives rise to binary semiconductors CdS and PbS, respectively. The impregnation step is driven by interactions between the precursors and active sites located at glass pore surfaces. After completing the impregnation–decomposition cycle, it was found that the active glass sites were regenerated, making new cycles possible. The amount of encapsulated semiconductor increases linearly as a function of the number of cycles. Nanocomposites obtained after 1–10 cycles were prepared and characterized by optical spectroscopy, X-ray diffraction powder and transmission electron microscopy. 相似文献
73.
《Thin solid films》2006,515(2):615-618
Silver tantalate AgTaO3 (ATO) and silver niobate AgNbO3 (ANO) films have been grown on to the LaAlO3 (001) and sapphire Al2O3 (0112, r-cut) single crystals by pulsed laser deposition technique from stoichiometric ATO and ANO targets. X-ray diffraction study revealed epitaxial quality of ATO and ANO films on the LaAlO3 (001) whereas on the sapphire r-cut substrate they are preferential (110) and (001) oriented. To characterize microwave films properties in the range from 1 to 40 GHz, coplanar line interdigital capacitors were fabricated by photolithography and lift-off technique. ANO film capacitors show superior properties: frequency dispersion was as low as 13%, voltage tunability (40 V, 200 kV/cm) was about 4.6% at 20 GHz, loss tangent ∼0.106 at 20 GHz, K-factor = tunability / tanδ from 49% @ 10 GHz to 33% at 40 GHz. 相似文献
74.
《International Journal of Impact Engineering》2006,32(5):702-724
The energy absorption potential of high-pressure die cast (HPDC) components made of magnesium alloys AM20, AM50, AM60, AZ91 and the aluminium alloy A356 is investigated using a shear–bolt principle. Both quasi-static and dynamic tests have been performed. In addition, single cast plates of AM60 and A356 alloy with different thickness have been tested in order to investigate the effect of plate thickness on the shear–bolt mechanism. It is found that this deformation principle gives an approximately constant average force during the deformation process. Therefore, thin-walled HPDC components can be suitable as energy absorbing components when using the shear–bolt principle. A simple empirical model for prediction of the average shearing force as a function of plate thickness and bolt diameter is proposed. 相似文献
75.
《Materials science & engineering. C, Materials for biological applications》2006,26(8):1451-1455
In this paper, a transmission electron microscopy (TEM) study was carried out to investigate the ability of magnetic nanoparticles (MNPs) to target breast cancer cells in mice. MNPs were functionalized using Luteinizing Hormone Releasing Hormone (LHRH), whose receptors are expressed in most types of breast cancer cells. LHRH conjugated MNPs (LHRH-MNPs) were injected intravenously into female nude mice bearing MDA-MB-435S.luc tumors for thirty days. These mice were sacrificed 20 h after MNP injection. Tumors and periphery organs including livers, lungs and kidneys were collected for analysis. A dedicated transmission electron microscopy (TEM) study was then carried out to investigate the distribution of nanoparticles in cells. We found that dispersive LHRH-MNPs were distributed in tumor cells and cells in lungs and livers. No LHRH-MNPs were observed in kidney cells. Furthermore, LHRH-MNPs tend to aggregate and form clusters in tumor cells and cells in lungs where metastases were developed. These suggest that MNPs functionalized using LHRH can be used to target both primary cancer cells and the metastatic cells. The study also indicates that TEM is a useful tool to study the sub-cellular distribution of functionalized magnetic nanoparticles in mice bearing breast cancers. 相似文献
76.
Dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing 总被引:1,自引:0,他引:1
Byoungchul Hwang Yang Gon Kim Han Sang Lee Sunghak Lee Byoung Doo Ahn Dong Hyuk Shin Chang Gil Lee 《Metallurgical and Materials Transactions A》2005,36(2):389-397
The dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing (ECAP)
was investigated in this study. Dynamic torsional tests, using a torsional Kolsky bar, were conducted on four steel specimens,
two of which were annealed at 480 °C after ECAP, and then the test data were compared in terms of microstructures, tensile
properties, and adiabatic shear-band formation. The equal-channel angular pressed specimen consisted of very fine, equiaxed
grains of 0.2 to 0.3 μm in size, which were slightly coarsened after annealing. The dynamic torsional test results indicated that maximum shear
stress decreased with increasing annealing time, whereas fracture shear strain increased. Some adiabatic shear bands were
observed at the gage center of the dynamically deformed torsional specimen. Their width was smaller in the equal-channel angular
pressed specimen than in the 1-hour-annealed specimen, but they were not found in the 24-hour-annealed specimen. Ultrafine,
equiaxed grains of 0.05 to 0.2 μm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries.
These phenomena were explained by dynamic recrystallization due to a highly localized plastic strain and temperature rise
during dynamic deformation. 相似文献
77.
《Materials Letters》2005,59(14-15):1845-1848
The recent tragedy of the Columbia shuttle has drawn much attention to the potential damage that may result from high velocity impact of foam on structural components. For obvious reasons, the emphasis was put on the structure rather than on the foam itself. We performed impact tests of polyurethane foam cylinders on various metallic plates, using small lightweight (m≈1.4 gr) cylinders launched at velocities in the range of 235–280 m/s. In addition to the resulting structural damage, we observed a peculiar and previously unreported failure mode for this kind of foam, which bears a high similarity to adiabatic shear failure. In this paper, we describe and discuss the essential results of the study with emphasis on the new failure mechanism for dynamically loaded polymeric foam. 相似文献
78.
After the nucleation and sedimentation of primary Fe-rich phases, the microstructures of Al-11.5Si-0.4Mg cast alloys with
0.35–1.03Fe and 0.18–0.59Mn have been studied to investigate the solidification characteristics of Fe-rich phases. Depending
on the iron and manganese contents as well as cooling rates, Fe-rich phases may solidify as predendritic (primary), pre-eutectic,
coeutectic, and posteutectic intermetallics at the different stages of solidification through three types of reactions: (1)
predendritic (primary), (2) eutectic, and (3) peritectic reactions. It seems that Fe-rich phases may nucleate on the wetted
sides of double oxide films, while the gap of the dry sides of oxide films constitutes the cracks commonly observed in the
Fe-rich phases and aluminum matrix. Conventional metallurgical observations also suggest that the Fe-rich phases nucleated
early during the solidification might act as nuclei for those formed subsequently, although it has not been ruled out that
these phases may share the same oxide substrates. It is probable that these nucleation events may all work as suggested in
the possible nucleation hierarchy for Al-11.5Si-0.4Mg cast alloys. 相似文献
79.
80.