1,720,988 research outputs found
Friction and wear behavior of magnetron co-sputtered V-Si-N coatings
No full textCutting tool life can be extended by using coatings, and that presents many opportunities to reduce manufacturing cost. In this study, V-Si-N coatings with 3.1 and 4.4 at% Si were prepared on high speed steel substrates (HSS) by reactive magnetron co-sputtering deposition. In addition to characterizing the microstructure, mechanical properties, and coating adhesion, the sliding friction and wear behavior were investigated. The V-Si-N coatings exhibited a dense growth structure, high nano-indentation hardness ( > 30 GPa) and good scratch adhesion (critical load > 80 N). Unlubricated ball-on-plate tribological tests were performed against Al2O3 or WC-Co counterparts at room temperature. Wear tracks were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray spectrometry (EDX). Under a normal load of 5 N, the friction coefficients against Al2O3 or WC-Co were less than 0.5, and the specific wear rates were in the range of 10(-8) mm(3)/N m. There was no obvious effect of relative humidity (RH) on the friction and wear behavior in the range of 30-80% RH. Mild wear continued up to similar to 10(5) sliding cycles, corresponding to a layer-by-layer removal mechanism. When the load was doubled to 10 N, a transition from mild to severe wear occurred after about 10(4) sliding cycles. Cracking and spallation increased at this point. It is suggested that a combination of rich V content and nanocomposite microstructure favors the excellent wear resistance of Vi-Si-N hard coatings. (C) 2014 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Hard and wear resistant VB2 coatings deposited by pulsed DC magnetron sputtering
No full textVanadium boride (VB2) coatings have been less concerned, although they have advantages of super hardness as well as self-lubrication. In this study, VB2 coatings were deposited by pulsed DC magnetron sputtering, and the effect of deposition parameters on the microstructure, mechanical and tribological properties of coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nano- and micro-indentation, and ball-on-disk tribometer. Under the growth condition with high adatom mobility, the coatings exhibited complete (001) orientation and dense texture. A nanocomposite structure that nanocolumns were separated by a secondary phase was especially observed in the coating deposited at 773 K. Both hardness and intrinsic stress of the coatings were improved substantially by increasing the substrate bias or the pulse frequency. The coating deposited at-30 V and 250 kHz, had the hardness of similar to 43.6 GPa and the compressive stress of similar to 2.0 GPa. Under the load of 2 N, the friction coefficients were similar to 0.7 against Al2O3 counterpart, and the wear rates were in the range of 7 x 10(-16)-8 x 10(-16) m(3)/N m. Under the load of 5 N, the coatings with low intrinsic stress showed better wear resistance, with the wear rate of 10(-16) m(3)/N m. (C) 2016 Published by Elsevier Ltd
Synthesis and Mechanical Properties of VB_2 Coatings by Pulsed Magnetron Sputtering
No full textThe VB_2 coatings were synthesized by pulsed magnetron co-sputtering on the substrates of Si(100), glass and M2 tool steel, pre-deposited with Ti transition layers. The impact of the frequency of power-supply on the microstructures and mechanical properties of the VB2 coatings was investigated. The VB_2 coatings were characterized with X-ray diffraction,scanning electron microscopy, atomic force microscopy and conventional mechanical probes. The results show that depending on the frequency,the VB_2 coatings possess improved surface mechanical properties, such as higher hardness, better wear-resistance and lower friction coefficient. As the frequency increased, the surfaces with big columnar-structured grains turned into amorphous-like surfaces with smaller grains and reduced roughness. Grown at 250 kHz, the preferentially oriented, smooth and compact VB2 coatings had a surface hardness of 43 GPa,and a wear-rate of 7.8 * 10~(-16) m3/N m,300 times lower than that of M2 tool steel
Achieving very low wear rates in binary transition-metal nitrides: The case of magnetron sputtered dense and highly oriented VN coatings
No full textThe monolithic binary transition-metal nitride coatings are easy to prepare but typically suffer from a high wear rate (typically far greater than 10(-16) m(3)/N m). Here we report a mechanistic investigation the wear behavior of vanadium nitride (VN) coatings which achieved wear rates on the 10(-17) m(3)/N m order of magnitude. The VN coatings were reactively magnetron sputtered at 773 K with relatively strong ion bombardment. The wear behavior was studied by ball-on-plate sliding tests, followed by microscopic examination using scanning electron microscopy (SEM) and atomic force microscopy (AFM), and chemical study by site-specific micro-Raman spectroscopy. Dense and highly oriented columnar VN coatings, 25-30 GPa in hardness, were obtained. Both coatings retained subsurface structural integrity after 1000 m sliding, and exhibited very low wear rates (<5 x 10(-17) m(3)/N m). The worn surface was very smooth, free of grooves and cracks in SEM, while fine features such as even platelets and infrequent nano-plowing events were identified by AFM. Meanwhile, chemical analysis of the worn surface identified the formation of V2O5-rich debris. These results point to the layer-by-layer wear mechanism, for which we proposed a scenario to account for some features of our microscopic observations. (C) 2014 Elsevier B.V. All rights reserved
Ga-doped ZnO films magnetron sputtered at ultralow discharge voltages: Significance of controlling defect generation
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Tribological behavior of VC/Ni multilayer coatings prepared by non-reactive magnetron sputtering
No full textCeramic-metal multilayer coatings generally exhibit considerably enhanced wear resistance, due to an attractive combination of metal and ceramic phases. In this work, VC/Ni multilayer coatings were prepared with non-reactive magnetron sputtering. Tribological behavior of the coatings was investigated by ball-on-plate dry sliding tests, followed by in-depth microscopic examination of the worn surfaces. The VC/Ni multilayer coatings exhibited the wear rates of 10-(15) m(3)/N m that was lowered by one order of magnitude in comparison with M2 tool steel. The results revealed that the wear process of coatings was influenced by the modulation period, and might further indicate that a sufficient thickness of hard layers was required to enhance the deformation resistance for optimizing the wear resistance of ceramic-metal multilayer coatings. (C) 2016 Published by Elsevier Ltd
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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