Metastable and Nanostructured Materials III

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Authors: S.A. Loureiro, Daniel Fruchart, Sophie Rivoirard, Dílson S. dos Santos, L.M. Tavares
Abstract: Zircaloy is commonly applied as structural element in nuclear reactors owing to the gamma radiation transparency of Zr. One of the research interests in Zr-Nb alloys is related to its behavior in H2O-rich environments due to hydrogen embrittlement. In the present work the microstructural evolution (crystallite size and microhardness), crystallography and hydrogenation behavior (after milling) due to mechanical alloying (MA) are studied for the Zr-Nb5%at and pure Zr. The MA study of Zr and the Zr-Nb system showed that frequency of rotation in a planetary mill and alloy composition play a major role on the evolution of crystallite size and microhardness. Nb addition was found to induce a partial allotropic transformation of the Zr structure (α→ω) during MA. Indeed, for milling experiments with significant Fe contamination the formation of an fcc phase was observed. Further, MA for extended times (over 5 hours) was found to reduce the hydrogen absorption capacity of Zr and the Zr-Nb system studied.
Authors: N.E. Skryabina, Daniel Fruchart, L. Cagnon, A.V. Shelyakov
Abstract: The creep deformation process initiated by hydrogen in both amorphous and nanocrystalline TiNi based alloys has been investigated. The mechanical behaviour has been interpreted in terms of microstructure phase transformations.
Authors: Marcelo R. Esquivel, Gabriel Meyer
Abstract: Mechanical milling (MM) and a combination of MM and temperature heating were used to synthesize the intermetallic MmNi5 and a MmNi5-Ni mixture, respectively. The process evolution with time was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM was used to characterize size and morphology of particles in order to reveal the governing mechanisms during the milling of each system. X-ray diffraction (XRD) was utilized to determine strain and crystallite size changes introduced by milling. The effects of integrated milling time on the sorption properties of the MmNi5-Ni mixture were analyzed. Results were correlated to defects introduced into microstructure. A comparison of the final characteristics of alloys obtained in each case is also shown.
Authors: Eleonora Erdmann, Marcos Lopes Dias, Victor Jayme Roget Rodriguez Pita, Fernanda Monasterio, Delicia Acosta, Hugo Alberto Destéfanis
Abstract: This paper shows the importance of the clay surface chemistry in the preparation of nanocomposite materials. An Argentinean montmorillonite was used for preparing two modified clays. The filosilicate was intercalated with a quaternary ammonium salt derived from ε- caprolactam to obtain an organofilic material. The other modification was introduced by mixing the clay with hexadecyl trimethyl ammonium chloride. Thus, the polyamide 6 ability in dispersing clays was applied to prepare composites with the intercalated clays. The polyamide 6/clay dry composites with 3 wt % of filler were prepared by melt processing in a mixer chamber. Composites of polyamide 6/organoclay were characterized by X-ray diffraction, transmission and scanning electron microscopy and thermogravimetry. The barrier properties were determined by cyclohexane pervaporation. The results show that the dispersion and degree of delamination depend on a proper chemical treatment and the clay content influences the polyamide 6 nanocomposites solvent pervaporation resistance.
Authors: Ho Chang, Mu Jung Kao, Shih Chieh Lin, Dao Yi Huang
Abstract: In this study, the author uses the self-developed submerged arc nanofluid synthesis system to fabricate TiO2 nanofluids. This system uses the energy produced by arc discharge to melt and vaporize matallic polarities under a vacuum condition. The vaporized metal is cooled rapidly inside a low-temperature dielectric liquid, forming nanoparticles that are evenly distributed inside the dielectic liquid. Experiment proves that the roundness of the fabricated TiO2nanoparticles are much better than those fabricated by aerosol methods. Also, the fabricated nanofluid carries a high suspension stability. We uses X-ray absorption spectroscopy to analyze their electronic structure of TiO2 nanofluid. Besides, by measuring the Zeta potential of TiO2 nanofluid having different pH values, it investigates into the suspension stability of the TiO2nanofluid. In order to verify the applicability of the TiO2nanofluid, this study also analyzes and compares the rheology properties of the nanofluid having different average particle sizes as well as their reaction towards light absorption.
Authors: M.M. Peres, J.B. Fogagnolo, Fernando Audebert, F. Saporiti, Alberto Moreira Jorge, Claudio Shyinti Kiminami, Walter José Botta Filho, Claudemiro Bolfarini
Abstract: A nanostructured aluminium alloy powder, prepared by rapid solidification via gas atomization, was consolidated into bulk material under various processing conditions via hot extrusion. The microstructure modifications and mechanical properties of the consolidated alloys as a function of the extrusion conditions were investigated. The increase in the extrusion-load with the increase of extrusion-rate and decrease of temperature are shown and discussed in association with the modification in the microstructures. The differences in mechanical properties measured by compressive tests are also discussed in association with the extrusion parameters. Furthermore, suggestions are given for rationalising the extrusion ratio and temperature conditions for the consolidation of nanostructured aluminium alloy powders via hot extrusion.
Authors: M.M. Peres, J.B. Fogagnolo, Alberto Moreira Jorge, Claudio Shyinti Kiminami, Walter José Botta Filho, Claudemiro Bolfarini
Abstract: Nanostructured aluminium-based alloys are light yet much stronger than conventional materials, which offer technological opportunities for applications such as in aerospace industry. One of the alloys of great interest for such applications is based on Al-Cu system and one of the main challenges for development of such alloys are associated with powder processing. However, processing such powder alloys into bulk material requires relatively low temperature and high pressure, which presents significant processing difficulties. A two-step approach is being explored in our group to reach the goal of a fully dense bulk material. Firstly, cold pressing is used to partially consolidate the powder material and secondly, hot extrusion is used to consolidate the alloy to full density. Process modelling is being used to design the extrusion process, including the extrusion ratio and extrusion length, to limit the temperature increase during extrusion as a result of adiabatic heating, and to avoid excessive heating to limit the undesirable grain growth of the material. A parametric study of extrusion parameters is presented and processing parameters are recommended. The use of process modelling has proven to be a useful tool in understanding the results from the extrusion experiments and limiting the number of interactions during extrusion.
Authors: C. Triveño Rios, Claudemiro Bolfarini, Walter José Botta Filho, Claudio Shyinti Kiminami
Abstract: Rapid solidification processes, RSP, are powerful tools to induce microstructural modifications, which may improve mechanical properties of alloys. In this paper the influence of rapid solidification on the formation of the undesirable brittle intermetallic compounds promoted by Si and Fe in Al-6Si-3Cu (A319-type) alloy have been investigated. The alloy have been casted using both conventional method and water-cooled wedge-copper mould. The microstructures have been evaluated by using a combination of X-ray diffraction, optical, scanning and transmission electron microscopy, and by Vickers microhardness. By increasing the cooling rate the length of the intermetallic β-Al5FeSi phase decreased, accompanying the same tendency of the secondary dendritic arm spacing. These results are accompanied by an increasing in hardness. Moreover, the formation and growth of the Al2Cu phase have been suppressed. These microstructural and hardness changes with the rapid solidification might be attributed to the increased solid solution content of the elements in the Al matrix.
Authors: T. Lilly Shanker Rao, Kirit N. Lad, Heena Dhurandhar, Arun Pratap, Prafulla K. Jha
Abstract: Soft magnetic alloys consisting of nanoscale fcc Fe grains have been developed by primary crystallization of melt-spun amorphous alloys as typically exemplified in Fe-B[1], Fe-M-B (M = Zr, Hf, Nb) (Nanoperm) [2] and Fe-Si-B-Nb-Cu (FINEMET)systems[3]. Lot of scientific effort has been put in last years to control the crystallization process of metallic glasses. This is due to the fact that several attractive properties of the resulting material are strongly related to the final attained microstructure. In the present paper, primary nanocrystallization kinetics of a Fe–based multicomponent amorphous system namely Fe67Co18B14Si1 (2605CO) has been analysed by nonisothermal DSC measurements. Crystallization is a combined process of nucleation and growth. The amorphous alloy undergoes two-step crystallization with primary crystallization of α-Fe giving the first step. The Avrami exponent for the two steps has been derived. A detailed analysis of the data provides an insight in to the dimensionality and mechanism of growth.
Authors: A.J.B. Dutra, I.C.F. Almeida
Abstract: Electrolytic manganese dioxide (EMD) nucleation and growth on titanium substrates from acidic manganese sulfate solutions was studied at 65oC and 90oC at different potentials and sulfuric acid concentrations. Electrochemical experiments allied to SEM examination were performed to characterize the mechanism of nucleation and its evolution with time. The EMD powder produced after a constant charge electrolysis of 448 mA·h was analyzed by SEM, BET, DTA/TG and X-ray diffraction. Results indicated that depending on the experimental conditions nucleation can be either progressive or instantaneous and when three-dimensional nuclei were formed the manganese dioxide deposit presented a higher specific surface area. Surface areas ranging from 51.8 to 168.8 m2/g were obtained under the conditions tested.

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