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Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. S...
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Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. Simulation results show that, for step flow growth, with the decrease of terrace width, the competition for feeding atoms between neighboring steps causes growth rate vs. step density to deviate from a linear relationship, and finally converge to a finite value. The step crystal direction also strongly influences the growth kinetics: vicinal surface with steps along the closest packed direction— [111] grows slower than that with [001] step. For island growth on terrace, the growth exponent of each layer in multi-layer island gradually transits from 1/2 for the top layer to 1/3 for the bottom layer, which demonstrates the transition from global diffusion controlled growth for top layer to surface diffusion controlled growth for bottom layer. The growth mechanism selection map with respect to terrace width and supersaturation is summarized and atom attaching rates of different growth mechanisms are also compared.
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The structural and electronic properties of Cu segregation in aluminum are studied in the framework of the density functional theory, within the projector augmented plane-wave method and both its local density approximation (LDA) ...
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The structural and electronic properties of Cu segregation in aluminum are studied in the framework of the density functional theory, within the projector augmented plane-wave method and both its local density approximation (LDA) and generalized gradient approximation (GGA). We first studied Al-Cu interactions in bulk phase at low copper concentration (≤3.12%: at). We conclude to a tendency to the formation of a solid solution at T=0 K. We moreover investigated surface alloy properties for varying compositions of a Cu doped Al layer in the (111) Al surface then buried in an (111) Al slab. Calculated segregation energies show unstable systems when Cu atoms are in the surface position (position 1). In the absence of ordering effects for Cu atoms in a layer (x_(Cu) = 1/9 and x_(Cu) = 1/3), the system is more stable when the doped layer is buried one layer under the surface (position 2), whereas for x_(Cu) = l/2 to x(cu) = l (full monolayer), the doped layer is more accommodated when buried in the sub-sub-surface (position 3). First stage formation of GP1- and GP2-zones was finally modeled by doping (100) Al layers with Cu clusters in a (111) Al slab, in the surface then buried one and two layers under the surface. These multilayer clusters are more stable when buried one layer beneath the surface. Systems modeling GP1-zones are more stable than systems modeling GP2-zones. However the segregation of a full copper (100) monolayer in an (100) Al matrix shows a copper segregation deep in the bulk with a segregation barrier. Our results fit clearly into a picture of energetics and geometrical properties dominated by preferential tendency to Cu clustering close to the (111) Al surface.
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A thermal model based on heat-conduction equation and Hertz-Knudsen equation for vaporization has been employed to simulate nanosecond pulsed laser based ablation of alumina. Heat transfer in the laser irradiated target with allow...
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A thermal model based on heat-conduction equation and Hertz-Knudsen equation for vaporization has been employed to simulate nanosecond pulsed laser based ablation of alumina. Heat transfer in the laser irradiated target with allowance for phase transitions, provides estimates for temperature distribution within the target and material ejection rate via ablation. Good agreement between calculated and experimentally measured data on mass ablation rate per pulse and its dependence on incident laser fluence from 5 to 22 J/cm(2), validated our theoretical model. Observed deviation between calculated and experimentally measured ablation rates at high average laser fluence levels was explained by ablation induced progressive degradation of target surface. Absence of abrupt increase in ablation rate with increased laser fluence suggested material ejection largely via normal boiling rather than explosive boiling mechanism. Calculated maximum surface temperature of the target was found to lie well below empirically estimated thermodynamic critical temperature for alumina, corroborating our observations on absence of onset of explosive boiling in alumina target on laser irradiation. Our simulation study enables proper selection of laser fluence, successfully minimizing laser induced target damage, as well as, degradation of micro-structural and mechanical properties of alumina films deposited via pulsed laser ablation. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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The surface roughness is one of the most important parameters which determines the functional properties and quality of machined parts. For that reason, the aim of this study is to investigate the effect of machining parameters on...
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The surface roughness is one of the most important parameters which determines the functional properties and quality of machined parts. For that reason, the aim of this study is to investigate the effect of machining parameters on the surface roughness for milling of biocompatible titanium alloy Ti6Al4V. In addition, optimization of cutting parameters was performed in order to achieve minimum surface roughness. The Taguchi method was used to find optimal values and analyze the effect of cutting parameters on the surface roughness. Three machining parameters, namely cutting speed, feed rate and depth of cut were observed in this paper. The analysis of the results reveal that the cutting speed has the biggest effect on the surface roughness for milling of biocompatible titanium alloy Ti6Al4V. Finally, a linear relationship between the observed cutting parameters and the surface roughness was determined.
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Enhanced ion beam etching and chemical etching of sapphire damaged by ion implantation have been investigated. In our experiments an amorphous layer or a damaged layer were produced respectively by high-dose yttrium ion or platinu...
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Enhanced ion beam etching and chemical etching of sapphire damaged by ion implantation have been investigated. In our experiments an amorphous layer or a damaged layer were produced respectively by high-dose yttrium ion or platinum ion implantation. Rutherford backscattering spectrometry and channelling (RBS-C) was used to analyse the material removed by ion beam etching or chemical etching. For 500 eV Ar ion beam etching, the etching rate for amorphous sapphire was 1.5 times faster than for single-crystalline sapphire. For chemical etching the etchant was acid solution of HCl-HF-H2O. Etching for 10 min removed a 150 nm thick amorphous layer, while only about 62 nm of the damaged layer (non-amorphous) was removed, and no visible change was observed for single-crystalline sapphire. [References: 14]
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Stacking faults along the (111) direction in low-temperature metastable aluminum oxide (eta-Al2O3 and chi-Al2O3) are studied using density functional theory (DFT). The surface energy of Al2O3 (111) is calculated; the intermediate ...
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Stacking faults along the (111) direction in low-temperature metastable aluminum oxide (eta-Al2O3 and chi-Al2O3) are studied using density functional theory (DFT). The surface energy of Al2O3 (111) is calculated; the intermediate layer between crystalline domains is considered; the Al-27 nuclear quadrupole coupling constants are determined.
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In this paper, the effect of the mechanical properties of aluminum alloys, cutting speed, feed rate and the drill diameter on burr height and surface roughness of drilling holes were investigated, using the Taguchi method. Al-2024...
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In this paper, the effect of the mechanical properties of aluminum alloys, cutting speed, feed rate and the drill diameter on burr height and surface roughness of drilling holes were investigated, using the Taguchi method. Al-2024, Al-7075 and Al-7050 were selected as the workpiece materials for experiments. The analysis of variance and signal-to-noise ratio were employed to analyze the effect of the drilling parameters. The results of the statistical analysis indicated that feed rate and cutting speed minimize significantly both the height of the exit burrs and the surface roughness. Moreover, the mechanical properties of the workpieces are different influential factors on both responses.
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The ever-growing market of electric vehicles and the upcoming grid-scale storage systems have stimulated the fast growth of renewable energy storage technologies. Aluminum-based batteries are considered one of the most promising a...
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The ever-growing market of electric vehicles and the upcoming grid-scale storage systems have stimulated the fast growth of renewable energy storage technologies. Aluminum-based batteries are considered one of the most promising alternatives to complement or possibly replace the current lithium-ion batteries owing to their high specific capacity, good safety, low cost, light weight, and abundant reserves of Al. However, the anode problems in primary and secondary Al batteries, such as, self-corrosion, passive film, and volume expansion, severely limit the batteries' practical performance, thus hindering their commercialization. Herein, an overview of the currently emerged Al-based batteries is provided, that primarily focus on the recent research progress for Al anodes in both primary and rechargeable systems. The anode reaction mechanisms and problems in various Al-based batteries are discussed, and various strategies to overcome the challenges of Al anodes, including surface oxidation, self-corrosion, volume expansion, and dendrite growth, are systematically summarized. Finally, future research perspectives toward advanced Al batteries with higher performance and better safety are presented.
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Surface-nitrided layers of Ti–6Al–4V alloy were fabricated using a diode laser in pure and mixed gas atmospheres of nitrogen and argon. The surface morphology, microstructure, hardness, and cracks of the nitrided layers were inv...
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Surface-nitrided layers of Ti–6Al–4V alloy were fabricated using a diode laser in pure and mixed gas atmospheres of nitrogen and argon. The surface morphology, microstructure, hardness, and cracks of the nitrided layers were investigated. In all gas atmospheres, the layers showed smooth and humped regions, and consisted of planar nitrogen titanium (TiN), dendrites, and acicular martensite. The surface roughness was improved dramatically as the nitrogen concentration of the atmosphere was diluted with argon. Overall, the hardness of the nitrided layer was greatest for pure nitrogen and it tended to decrease as the concentration of argon in the atmosphere increased. However, the hardness of the layer for pure nitrogen also decreased rapidly, from the surface to matrix, in comparison to the diluted nitrogen atmospheres. It was shown that the number and size of dendrites, which determine hardness, are controlled by the nitrogen concentration. The dendrites of the nitrided layer were denser and smaller in a pure nitrogen atmosphere, than in diluted nitrogen atmospheres. Longitudinal and transverse cracks were observed in the nitrided layers. These two types of cracks were decreased or even eliminated as the argon concentration of the nitrogen–argon atmosphere was increased. Therefore, by diluting the nitrogen atmosphere with argon, the nitrided layer properties, in terms of surface roughness and cracks, can be improved, but this may also cause a reduction in the layer hardness.
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Al-based coagulants are widely used in water treatment plants, and residual Al has detrimental effects on human health. Response surface method (RSM) was used to investigate the residual Al produced in the coagulation process. Alu...
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Al-based coagulants are widely used in water treatment plants, and residual Al has detrimental effects on human health. Response surface method (RSM) was used to investigate the residual Al produced in the coagulation process. Aluminum sulfide (Al_2(SO_4)_3· 18H_2O) (AS) or polyaluminum chloride (PACl) and high performance polyaluminum chloride (HPAC) were used as coagulants. Fe-surface modified TiO_2 (100mg/L) and Al_2O_3 (100mg/L), after mixing with AS, were used as another two new coagulants. The results indicated that PACl and HPAC produced lower dissolved residual Al than AS in most experimental conditions, but AS produced the lowest dissolved residual Al (0.07 mg/L) under the optimum pH value (6.83). Al_a may have significant effects on dissolved residual Al. Alb formed in situ performed more efficiently than pre-hydrolyzed Alb. The results of HPSEC and 3D-EEM indicated that the addition of nanoparticles could increase the removal efficiency of organic matter in the solution, and the concentration of organic matter with molecular weight smaller than 1500 Da was decreased. The residual Al with a MW range of 0-1.0 kDa was of a larger portion in all water samples. The element mapping proved that the nanoparticles connected the particles together as a bridge, resulting that the floc size after re-growth with nanoparticles remains larger than when using AS.
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