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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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    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.
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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.
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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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  • 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.
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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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  • 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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    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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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 17
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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.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 18
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    Microstructure and mechanical properties of vacuum induction melted as-cast 43Ni-29Fe-18W-10Co matrix alloy (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): A. Sambasiva Rao, Premkumar Manda, M.K. Mohan, A.K. Singh Present work describes a correlation among microstructure, texture, tensile flow and work hardening behavior of alloy 43Ni-29Fe-18W-10Co in as-cast condition prepared by induction melting technique. The microstructure of the alloy exhibit single fcc (γ) phase along with the characteristic dendritic features. The bulk texture of the as-cast alloy displays the presence of triclinic sample symmetry and typical nature of coarse grained materials. Present alloy shows moderate in-plane anisotropy (A IP ) and reasonably low anisotropic index (δ) values. The true stress-true plastic strain curves show the evidence of two slopes at low and high strain regimes and follow typical Ludwigson constitutive equation. The work hardening curves illustrate the three distinctive stages (I, II and III). The addition of Co improves the strength and elongation values as well as influences the flow and work hardening behavior during tensile testing in comparison to those of other Ni-Fe-W matrix alloys.
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  • 19
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    Formation of chromium carbide coatings on HT250 steel by thermal diffusion processes in fluoride molten salt bath (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Xingzhi Su, Sufang Zhao, Juan Hou, Guojun Yu, Yanjun Chen, Hua Sun, Peng Zhang, Leidong Xie LiF-NaF-KF (46.5-11.5-42 mol %, FLiNaK) molten salt was used in the thermal diffusion (TD) process to form chromium carbide coatings on gray cast iron HT250 at 900 °C for 8 h. The structure and chemical composition of the coating were observed by scanning electron microscopy coupled with energy dispersive X-ray microanalysis (SEM-EDX) and X-ray diffraction (XRD). Both the nanoindentation hardness and Vickers hardness were measured. A 3–5 μm thick chromium carbides layer and approximately 10 μm thick transition layer were formed on the surface of gray cast iron HT250. The chromium carbides layer was composed of Cr 23 C 6 and Cr 7 C 3 . The hardness of gray cast iron HT250 was increased 6 times after treatment. The tribological behavior was also improved. These results demonstrate that fluoride salts can be used as base salts to form excellent chromium carbides coatings via the TD process.
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  • 20
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    Study of the metal-semiconductor contact to ZnO films (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Yu Yan, Wei Mi, Jinshi Zhao, Zhengchun Yang, Kailiang Zhang, Chongbiao Luan High resistance Zinc oxide (ZnO) films have been prepared on Si (100) substrates using magnetron sputtering method. Structure analysis revealed a clear out-of-plane orientation of ZnO (001) || Si (100). The metallic composition of the contact is a critically important parameter for making ohmic contacts to ZnO films. Al/Ti metal contacts show linear I-V characteristics indicative of ohmic behavior, while other metal contacts such as Al and Ti show nonlinear characteristics with rectification, that reveal the presence of schottky barriers.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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