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  • Articles  (2,870)
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  • 11
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    Investigation of laser-irradiated structure evolution and surface modification by in situ Micro-Raman spectroscopy (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-19
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Chao Li, Guoxiang Wang, Xianghua Zhang, Yawen Zhang The structure evolution and surface modification of the ZnSb, ZnSb-Bi and ZnSb-NiO phase-change films are detected by in situ Raman laser irradiation with the different laser power and irradiation time. The results show that undoped ZnSb films exhibit a phase transformation from amorphous to metastable phases at 250 mW. The Bi-doped ZnSb films exhibit two different crystallization behaviors as the laser power increases. The films containing low Bi-doping concentration exhibit an amorphous-to-metastable phase transition, while the films containing high Bi-doping concentration directly crystallize into a mixture of new Bi-related crystalline phases and metastable ZnSb phases. As for ZnO-doped ZnSb films, the structure evolution encounters an amorphous phase, metastable ZnSb phase or mixture of both. Identifying the structure evolution in the metastable phase by in-situ Raman measurement method is of great significance for phase change memory application.
    Print ISSN: 0042-207X
    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 12
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    Effect of HCl and NH4OH etching on CZTSSe absorber layer (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-17
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Vishvas kumar, Srinibasa Padhy, Arindam Basak, Udai P. Singh Cu 2 ZnSn (S x Se 1-x ) 4 thin films were deposited on glass substrates using the screen printing method. The structural, compositional and surface morphology characteristics were studied using XRD, EDXRF and Scanning electron microscopy (SEM) to determine its crystal, composition and surface morphology. The XRD pattern shows the presence of binary phases where Cu 2 Se is the most prominentphase among all. The presence of binary phases reduces the open-circuit voltage ( V OC ) and fill factor (FF) which in turn decreases the efficiency of the CZTSSe solar cells. The binary phases are removed by etching the film in HCl followed by NH 4 OH as observed from XRD pattern. The EDXRF result shows that the weight% of Cu reduces after etching and the SEM also confirms the removal of the over layer from the surface of the film.
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    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 13
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    Effects of annealing on quality and stoichiometry of HfO2 thin films grown by RF magnetron sputtering (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-17
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Arun Vinod, Mahendra Singh Rathore, N. Srinivasa Rao In this paper, the effects of annealing temperature on HfO 2 thin films prepared by RF sputtering have been investigated. Thin films of hafnium oxide were deposited using sputtering onto p-type Si substrates and the pristine films were annealed at different temperatures in air atmosphere to obtain crystallinity. The Raman and XRD results of the as-deposited films show amorphous nature, whereas the annealed films at 600 °C results in crystallization. AFM was used to study the surface morphology of the films and to estimate the skewness, kurtosis and the roughness values. The core level orbitals of Hf 4f spectra of as-deposited films not only reveal the formation of hafnium rich hafnium oxide but also nearly stoichiometric composition of HfO 2 and exhibit a shift in binding energy with annealing. Electrical measurements of the films suggest that the leakage current is increased for crystalline films as compared to the as-deposited ones. The effects of annealing temperature on quality and stoichiometry of hafnia thin films and their possible applications are reported.
    Print ISSN: 0042-207X
    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 14
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    Insight into the thermodynamic properties of tungsten disilicides (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-17
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Yong Pan, Yuanpeng Wu Thermodynamic properties play a crucial role in high-temperature materials. Although WSi 2 is a promising high-temperature material, the thermodynamic properties of WSi 2 are unknown. We apply the first-principles to investigate the melting-point, Debye temperature and heat capacity of WSi 2 . The calculated melting-point of the hexagonal C40 structure, tetragonal C11 b structure and orthorhombic C54 structure is 2256 K, 2559 K and 1856K, respectively. The calculated Debye temperature of WSi 2 follows the order of C40 > C11 b  > C54. The thermodynamic properties of WSi 2 derive from the vibration of the Si and Si-Si bond. However, the calculated heat capacity of C54 structure is larger than that of other structures.
    Print ISSN: 0042-207X
    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 15
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    Study of martensitic transformation in TiNiCuNb shape memory alloys using dynamic mechanical analysis (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-17
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): M.Y. Liu, W.Y. Qi, Y.X. Tong, B. Tian, F. Chen, L. Li In present work, effect of Nb content on martensitic transformation and damping behavior of (Ti 50 Ni 38 Cu 12 ) 100-x Nb x (x = 0, 5, 10, 15at.%) shape memory alloys was investigated by means of X-ray diffraction, differential scanning calorimetry and dynamic mechanical analysis. As a result, the transformation sequence of TiNiCuNb alloys is found to be B2→B19→B19′ upon cooling. Two different damping peaks are observed, one is related to B2→B19 transformation and the other one is related to the overlapping of twin relaxation-type and B19→B19′ transformation. With increasing Nb content to 15 at.%, the peak value of damping capacity of B2→B19 transformation slightly decreases.
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    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 16
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    A physically based constitutive model of As-forged 34CrNiMo6 steel and processing maps for hot working (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-17
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): B. Gong, X.W. Duan, J.S. Liu, J.J. Liu In this paper, isothermal compression tests of as-forged 34CrNiMo6 steel were carried out using a Gleeble–1500D testing machine for the deformation temperatures ranging from 1173 K to 1473 K and strain rates ranging from 0.005 s −1 to 1 s −1 . Flow stress curves were obtained under the given conditions. Using regression analysis, the hyperbolic sine law Zener–Hollomon equation was established, and the hot deformation activation energy was obtained as 376.5 kJ mol −1 . To predict the flow stress for hot working, a constitutive model including work hardening-dynamic recovery modeling and the corresponding Avrami–type dynamic recrystallization equation was established. The work hardening-dynamic recovery model was derived based on the evolution equation of the dislocation density and the work hardening rate. All parameters in this model can be expressed in terms of the Zener–Hollomon parameter. Our results indicated that the proposed constitutive model had high prediction accurately for hot working of as-forged 34CrNiMo6 steel. Furthermore, the optimized processing parameters for the as-forged 34CrNiMo6 alloy steel were determined based on the processing maps and microstructure.
    Print ISSN: 0042-207X
    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 17
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    Wear characteristics of hybrid aluminum-matrix composites reinforced with well-dispersed reduced graphene oxide nanosheets and silicon carbide particulates (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-17
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Xiang Zeng, Jingang Yu, Dingfa Fu, Hui Zhang, Jie Teng In the present study, hybrid composites consisting of a hypoeutectic aluminum-silicon (Al-Si) matrix with silicon carbide (SiCp) (10 wt%) and various reduced graphene oxide (RGO) (0.3–0.7 wt%) contents were fabricated using a combined solution-mixing and powder metallurgy (PM) route. The tribological behaviors of these composites against a GCr15 steel ball were studied under dry sliding-wear conditions using a ball-on-disc configuration. The effects of the RGO content and applied loads on the coefficient of friction (COF) and wear rates were evaluated. To study the wear mechanism, comprehensive characterization of the worn surfaces and debris was performed using scanning electron microscopy (SEM). In contrast with the Al-Si/SiCp composite, the hybrid Al-Si/SiCp/RGO composites showed reduced wear rates because of the stabilized COF, and the self-lubricating effects of the incorporated RGO. In the case of all the composites, the wear rate increased as the load increased. Delamination wear is the dominant wear mechanism of the Al-Si/SiCp composite, at both low and high loads. At low loads, the dominant wear mechanism of the Al-Si/SiCp/RGO hybrid composites is abrasive wear accompanied by adhesion wear; this transitions to delamination wear at high loads.
    Print ISSN: 0042-207X
    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 18
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    Influence of sulfurization time on two step grown SnS thin films (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): M. Gurubhaskar, Narayana Thota, M. Raghavender, G. Hema Chandra, P. Prathap, Y.P. Venkata Subbaiah SnS thin films were prepared using a simple two-stage process. The two-stage process involved in sputtering of Sn over glass substrate followed by sulfurization of sputtered Sn at 350 °C. The sulfurization process was carried out in the ambience of sulfur for different time lengths, 10–120 min and its influence on physical properties are reported. XRD study showed that the films sulfurized at 10 min were poor in crystallinity with reflections of un-reacted tin and sulfur. As the sulfurization time (S t ) is increased to 60 min, a single phase orthorhombic SnS was observed with (111) preferred plane. Four distinct Raman modes at 95, 163, 190 and 220 cm −1 confirms the formation of SnS for S t  > 30 min, however, S t  〈 30 min treated Sn films had extra Raman peak at 489 cm −1 related to S x phase. The ratio of Sn/S was found to be 2.92 for 10 min and reached stoichiometric ratio with densely packed grain morphology for 60 min. The optimized films showed a direct band-gap of 1.35 eV. The XPS oxidation states of Sn and S were found to be (+2) and (−2), indicating the formation of SnS. The S t dependent electrical measurements are also reported and discussed.
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  • 19
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    Theoretical parametric investigation of plasma sustained by traveling electromagnetic wave in coaxial configuration (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): T. Bogdanov, E. Benova The electromagnetic wave traveling along a dielectric–gas interface can produce and sustain gas discharge in various geometrical configurations. We propose a parametric study of surface-wave-sustained plasma in coaxial configuration at low pressure based on stationary 1.5D (1D for plasma density and 2D for the wave electromagnetic field components) model. At this configuration the plasma is produced outside a dielectric tube in a low pressure chamber when at the tube axis a metal antenna is arranged. The model gives the phase diagrams and the axial distribution of the plasma density, wave power, wave number, and wave field components, as well as the radial distribution of the wave field components. The dependence of wave and plasma characteristics on the geometry parameters (the plasma radius, the dielectric tube thickness, and the metal antenna radius) and on the dielectric tube permittivity is investigated and shown in this paper. The discharge conditions at which it is possible to sustain plasma by an azimuthally symmetric wave are obtained. Comparison with the cylindrical plasma in corresponding conditions and with experimental data is also presented.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 20
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    Study of rarefied gas flows in backward facing micro-step using Direct Simulation Monte Carlo (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Abhimanyu Gavasane, Amit Agrawal, Upendra Bhandarkar A backward facing micro-step is a building block for many microfluidic devices. Due to micron sized characteristic dimensions, the gas flow in such a geometry is rarefied in nature. Such rarefied gas flows are widely solved using the Direct Simulation Monte Carlo (DSMC) technique. Flow separation, circulation and re-attachment are some of the basic characteristics of step flows. The objective of this study is to analyze the effect of rarefaction on the flow properties and the separation of the flow. The range of selected Knudsen number (Kn) covers the slip and transition regime from a value of 0.0311–13.25. The pressure ratios employed are 3 and 5. It is observed that the slip velocity continuously increases while the centre-line velocity first decreases, then remains constant and finally increases with increase in Kn. At the step, separation of the flow is seen for Kn 〈 0.1325 while no such separation is observed in the range of Kn from 0.198 to 13.25. The corresponding Re for these ranges are 6.43 to 0.67 and 0.392 to 0.012 respectively. The re-attachment length decreases with increase in Kn whereas it increases with increase in Re. A stronger pressure force and a weaker diffusion effect leads to flow separation in the slip regime whereas stronger diffusion and weaker pressure force lead to an absence of flow separation in the transition regime. Finally, this work presents for the first time the existence of the Knudsen minimum for such a backward step geometry.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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