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991.
The intermetallic phase selection during homogenization in a AA6082 alloy has been investigated. A short homogenization treatment at 580?{\degr}C for 4?h and a subsequent slow cooling with a rate of about 8?{\degr}C/min, rather than a conventional quick quenching into water, results in the formation of the rounded discrete Al15(FeMnCr)3Si2 phase, which greatly suppressed the formation of the plate-shaped β-Al5FeSi phase. Most of the Al15(FeMnCr)3Si2 particles were observed to be very fine (about 200?nm) and homogeneously distributed in the α-Al matrix. Fine Mg2Si particles were also observed to be located in the vicinity of Al15(FeMnCr)3Si2 particles. Additionally, the β series precipitates (most likely β″-Mg2Si), large-scale U2-AlMgSi and B′ (type C) phases were also observed within the α-Al matrix. This investigation demonstrates that the size and distribution of the desired intermetallic phases can be influenced by suitable homogenization treatments. 相似文献
992.
AbstractThe evolution of dislocation density and microstructure of a hot rolled Zr–2.5Nb alloy under compressive plastic strain, at room temperature, was analysed using neutron diffraction and transmission electron microscopy (TEM). The dislocation densities of type 〈a〉, 〈c + a〉 and 〈c〉 dislocations at different plastic strains in the elastic–plastic transition regime and plastic regime have been measured by diffraction line profile analysis (DLPA). TEM microstructure characterization revealed the operation of different slip systems. It has been found that slip of type 〈a〉 dislocations contributed to most of the plastic strain at the early stage of deformation, and strong pyramidal 〈c + a〉 slip did not occur until the deformation was fully plastic. Unambiguous evidence of basal slip occurring at room temperature in Zr is provided. Loading along a plate direction with more basal poles favoured the operation of basal and pyramidal slip. Dislocation features including relative edge:screw character of 〈c + a〉 dislocations are shown to be different under tension and compression loading, providing a mechanistic driver for the previously observed asymmetry in critical resolved shear stress for 〈c + a〉 slip. 相似文献
993.
994.
Size effect on nanomechanical properties of ZnO cones using in situ transmission electron microscopy
Shao-Hui Kang Te-Hua Fang Tao-Hsing Chen Ching-Hong Kuo 《Current Applied Physics》2013,13(8):1689-1696
Nanoscale fracture and strain-induced structure variation of ZnO nanocones are determined using in situ transmission electron microscopy compression experiments. For the single-crystalline nanocones with diameters of 100–300 nm, the Young's modulus is in the range of 7.7–48 GPa and the ultimate tensile strength is in the range of 2.4–4.3%. The Young's modulus and tensile strength increase with decreasing diameter. Here, we report the nanogenerator of ZnO nanocones can be used mechanical energy to output 90 nW/mm2. 相似文献
995.
Asmahani Awang S.K. Ghoshal M.R. Sahar M. Reza Dousti Raja J. Amjad Fakhra Nawaz 《Current Applied Physics》2013,13(8):1813-1818
Glasses with composition 70TeO2–20ZnO–10Na2O–0.5Er2O3–(x)Au are synthesized by melt-quenching technique. Their spectroscopic and optical characterizations are made. The presence of gold nanoparticles (Au NPs) with average size ~9 nm is confirmed from TEM micrograph. The value of Edir is found to lie between 3.082 and 3.073 eV, while Eindir lies within 2.765 to 2.724 eV. The observed visible up-conversion (UC) emission under 779 nm excitation wavelength exhibits two bands centered at 546 nm (green) and 637 nm (red) in all samples. The glass with 0.4 mol% Au NPs shows dominant enhancement in the UC emission intensity of the order of 3.5 times for the green band (4S3/2 → 4I15/2) and a weaker enhancement for the red (4F9/2 → 4I15/2) band. The optical properties of the system are affirmed to depend strongly on the Au concentration in the dielectric medium. The absorption spectra consist of six bands attributed to absorption from ground state (4I15/2) to 4I13/2, 4I11/2, 4I9/2, 4F9/2, 2H11/2, and 4F7/2 excited states. The structural reveals that the types of bonding and difference in electro-negativity can be manipulated by the presence of metallic NPs in glass matrix. Judd–Ofelt analysis asserts the increase in Ω2 and Ω6 parameters with the addition of Au NPs and the enhancement of green and red emissions. The enhancement is mainly attributed to large plasmonic effect of Au NPs. The proposed glasses can be nominated as potential materials for solid state laser developments. 相似文献
996.
997.
The aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 mm to 12.5 μm. The influence of the thickness, grain size and ratio thickness to grain size on the mechanical properties and strain hardening were investigated by mechanical tests and TEM observations. The results show the presence of three different domains of mechanical behaviour: polycrystalline, multicrystalline and quasi-single crystalline depending on the thickness and on the number of grains across the thickness. The transition between the three domains is due to the occurrence of surface effects involving a decrease in the long-range internal backstress revealed by the TEM observations. 相似文献
998.
Effects of mobile-phase variations on the chromatographic separation on amino-bonded silica column in hydrophilic interaction chromatography (HILIC) were investigated for four zwitterionic tetracyclines (TCs): oxytetracycline, doxycycline, chlortetracycline, and tetracycline. A mixed-mode retention mechanism composed of partitioning, adsorption, and ion exchange interactions was proposed for the amino HILIC retention process. Buffer type and pH significantly influenced the retention of TCs, but showed similar separation selectivity for the tested analytes. Experiments varying buffer salt concentration and pH demonstrated the presence of ion exchange interactions in TCs retention. The type and concentration of organic modifier also affected the retention and selectivity of the analytes, providing direct evidence supporting the Alpert retention model for HILIC. The retention time of the analytes increased in the following order of organic modifiers: tetrahydrofuran < methanol < isopropanol < acetonitrile. The linear relationships of logk' versus %water (v/v) curve and logk' versus logarithm of %water (v/v) in the mobile phase indicated that TCs separation on the amino phase was controlled by partitioning and adsorption. The developed method was successfully utilized in the detection of TCs in both river water and wastewater samples using solid-phase extraction (SPE) for sample cleanup. 相似文献
999.
Brčić Karačonji I Zimić L Brajenović N Skender L 《Journal of separation science》2011,34(19):2726-2731
A headspace solid-phase microextraction method (HS-SPME) followed by gas chromatography with mass spectrometric detection (GC/MS) has been developed for the determination of low concentrations of nicotine in hair. Parameters affecting the SPME procedure including type of fiber coating, extraction mode, extraction temperature and time, desorption time, stirring, and salt addition have been evaluated and optimised. The method provided good linearity (r(2)≥0.9980) over the concentration range tested (0.2-20 ng/mg) and low detection limit (0.02 ng/mg). Precision expressed as relative standard deviation was <10%. The average accuracy was 95%. The proposed method was used to determine hair nicotine levels in 100 children in order to assess exposure to environmental tobacco smoke (ETS). The described HS-SPME procedure is fast, simple, sensitive, and solvent-free and is therefore suitable for studies involving ETS exposure assessment. 相似文献
1000.