Papers by Keyword: Nanocrystalline

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Authors: Paul J. Warren, M. Thuvander, M. Hourai, H. Lane, Alfred Cerezo, George D.W. Smith
Authors: Shubhra Mathur, Rishi Vyas, S.N. Dolia, Kanu Sachdev, S.K. Sharma
Abstract: Corrosion studies were carried out using potentiodynamic polarization method on amorphous, nanocrystalline and crystalline states of the alloy Ti60Ni40 in 0.5 M H2SO4 and 0.5 M HNO3 aqueous media at room temperature. The nanocrystalline state of Ti60Ni40 was obtained by removing about 10 μm from the air side surface (crystalline state) by polishing. The presence of nanocrystalline phase was confirmed by X-ray diffraction (XRD). It was found from polarization results that the corrosion current density was higher in the amorphous state than in the nanocrystalline state in both 0.5 M H2SO4 and 0.5 M HNO3 aqueous media. These results are corroborated by the weight loss studies which were carried out in both of these media. Results are discussed in the paper in the light of data reported in the literature on similar type of alloys.
Authors: Zi Ling Xie, Lin Zhu Sun, Fang Yang
Abstract: A theoretical model is developed to account for the effects of strain rate and temperature on the deformation behavior of ultrafine-grained fcc Cu. Three mechanisms, including dislocation slip, grain boundary diffusion, and grain boundary sliding are considered to contribute to the deformation response simultaneously. Numerical simulations show that the strain rate sensitivity increases with decreasing grain size and strain rate, and that the flow stress and tensile ductility increase with either increasing strain rate or decreasing deformation temperature.
Authors: Julia Ivanisenko, Ian MacLaren, Ruslan Valiev, Hans Jorg Fecht
Abstract: Recent studies of nanocrystalline materials have often found that the deformation mechanisms are radically different to those in coarse-grained materials, resulting in quite different mechanical properties for such materials. The use of pearlitic steels for the study of the deformation mechanisms in bcc materials with ultrafine grain sizes is quite convenient, because it is relatively straightforward to obtain a homogenous nanocrystalline structure with a mean grain size as small as 10 nm using various modes of severe plastic deformation (SPD). In this paper we show that highpressure torsion of an initially pearlitic steel results in a nanostructured steel in which austenite has been formed at or close to room temperature. The orientation relationship between neighboring ferrite and austenite grains is the well-known Kurdjumov-Sachs orientation relationship, i.e. the same observed in temperature-induced martensitic transformation of iron and steels. It is shown that this must have resulted from a reverse martensitic transformation promoted by the high shear strains experienced by the material during severe plastic deformation of the nanocrystalline structure. This transformation represents an alternative deformation mechanism that can be activated when conventional deformation mechanisms such as slip of lattice dislocations become exhausted.
Authors: Mustafa Zaien, Naser Mahmoud Ahmed, Hassan Zainuriah
Abstract: A nanocrystalline CdO thin film was successfully synthesized on p-type silicon substrate with approximately 370 nm thickness by a vapor transport process (solid-vapor deposition) for Cd powder at 1274 K with argon and oxygen flows in a tube furnace. Scanning electronmicroscopy revealed that the product was a CdO nanocrystalline. X-raydiffraction and energy dispersive X-ray techniques were used to characterize structural properties. The grown nanocrystalline thin film had a grain size of 38 nm. Photoluminescence spectroscopy was conducted to investigate the optical properties of the nanocrystalline CdO thin film. A strong emission peak was observed at 511 nm (2.43 eV), which is ascribable to the near-band-edge emission of CdO with a full-width and half maximum of approximately 124 nm. The sheet resistance and the resistivity of the CdO thin film were measured using a four-point probe; RS = 16.2 Ω/sqand ρ = 5.82×10-4 Ω.cm.Carrier concentration and Hall mobility were obtained by Hall-effect measurement system; n = 1.53×1020 cm-3 and μH = 42.3cm2/Vs.
Authors: Jin Song Chen, Yin Hui Huang, Bin Qiao, Jian Ming Yang, Yi Qiang He
Abstract: The principles of jet electrodeposition orientated by rapid prototyping were introduced. The nanocrystalline nickel parts with simple shape were fabricated using jet electrodeposition. The microstructure and phase transformation of nanocrystalline nickel were observed under the scanning microscope and X-ray diffraction instrument. The results show that the jet electrodeposition can greatly enhance the limited current density, fine crystalline particles and improve deposition quality. The nickel parts prepared by jet electrodeposition own a fine-grained structure (average grain size 25.6nm) with a smooth surface and high dimensional accuracy under the optimum processing parameters.
Authors: Wei Lv
Abstract: For the past few years, nanocrystalline soft magnetic alloy has become hot topic in the field of strategic functional materials based on its excellent magnetic properties and advantages of energy saving, low cost, etc. With rapid innovationof various new type soft magnetic materials, FeCuNbSiB soft magnetic powder cores havebeen gradually turning into researching focusin soft magnetic material field for its excellent high frequency properties, such as high magnetic permeability (μ) and quality factor (Q), low core loss (Pc) and coercivity (Hc), etc.This paper mainly reviews the recent advances and technological achievements of FeCuNbSiB nanocrystalline soft magnetic powder cores, and also provides a brief introduction of FeCuNbSiB/Mn-Zn ferrite powder core, one new type composite magnetic powder core. Finally, future developing trend for FeCuNbSiB nanocrystalline powder cores isalso prospectedcompendiouslyin the paper.
Authors: Y. Waku, Hideki Ohtsubo, Ki Buem Kim
Authors: F. Mazaleyrat, J. Bigot, J.C. Faugieres, J.F. Rialland
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