1,721,016 research outputs found
Influence of atmospheric pressure plasma treatments on the oxide film and the corrosion resistance of titanium and titanium alloy
No full textIn the industrial plants, plasma is often used for cleaning and activating the surfaces and/or for the formation of different types of coatings. In the past, the plasma technology required the use of low pressures with consequent economic and technological problems. The development of plasma technologies that can work at atmospheric pressure overcomes the disadvantages of traditional vacuum operation and permits to apply this technology in a larger number of applications for example in continuous in line manufacturing. In this study, the influence of a treatment carried out with an atmospheric pressure plasma jet (APPJ) on the passive oxide films of titanium and titanium alloys and the correlation between these changes and the corrosion properties were studied. The treatments were realized on commercially pure titanium (grade 1) and a Ti6A14V (grade 5) titanium alloy using a plasma generated by air at 1.5 bar. Different process parameters were tested. In detail, the effect of the distance plasma torch-sample and of the rate of movement of the plasma torch during the treatment (useful to simulate an in line continuous process) were studied. The corrosion resistance of the samples was analyzed with potentiodynamic polarization and electrochemical impedance spectroscopy tests, using as electrolyte the Ringer solution. The effects of the treatment on the oxide layer were studied using secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The plasma treatment allowed the growth of the passive film and improved the corrosion resistance of both titanium and titanium alloy
Microstructure and corrosion properties of PEO coatings produced on am-aluminum alloys
No full textAluminum alloys are one of the main materials employed in aerospace and automotive applications. One of the problems that affect these alloys in certain application is the poor corrosion resistance that can, however, be enhanced with proper surface treatments, such as anodizing. Among these treatments, Plasma Electrolytic Oxidation (PEO) is one of the most promising and the production of PEO coatings on traditional aluminum alloy was extensively studied in literature. Recently, the production of a lot of components is going into the direction of using innovative manufacturing systems and customized components, with improved mechanical and physical properties, can be manufactured by additive manufacturing (AM) techniques. Among the AM methods, laser-based AM has an immense potential for producing fully dense metallic structures, using a variety of available metal powders and has attracted more and more attention. The resulting AM samples are characterized by different microstructures in comparison with the conventionally manufactured ones and this can cause differences also in the production of PEO coatings and other surface treatments. Objective of the present work is to produce PEO coatings on AM samples in order to increase the corrosion and wear performances of the samples. PEO coating were produced on the samples testing different parameters and the coatings were characterized, in terms of microstructure and composition, with SEM analysis. The corrosion resistance of the samples was also evaluated with electrochemical tests. The results were compared with the ones obtained on traditionally manufactured samples. PEO coatings were successfully produced on AM samples obtaining samples with good coatings thickness and improved corrosion performances compared to the untreated ones
Influence of silicon morphology on direct current plasma electrolytic oxidation process in AlSi10Mg alloy produced with laser powder bed fusion
Full text linkIn this work, plasma electrolytic oxidation (PEO) process was applied on AlSi10Mg samples, produced with laser powder bed fusion (L-PBF), in the as printed condition and after different heat treatments, and, for comparison, on as-cast samples of AlSi10Mg. PEO process was performed in direct-current mode using high current densities and short time in a basic silicate electrolyte. For the first time, the effects of silicon morphology in L-PBF AlSi10Mg samples, in as printed condition and after different heat treatments, on the obtained PEO coating were investigated in terms of microstructure and corrosion properties. The microstructure of the substrate was characterized with optical and electron microscopy observations (optical microscopy OM, scanning electron microscopy SEM, and transmission electron microscopy TEM) and with X-ray diffraction (XRD). The analysis showed that heat treatments of annealing and solution treating modified the morphology and distribution of silicon in the samples obtained through L-PBF. The PEO coated samples were characterized with SEM, both on the surface and in the cross-section, and compositional analysis were performed with energy dispersive spectroscopy (EDS) analysis and elemental mapping. The coatings were also analyzed with XRD and the corrosion properties evaluated through electrochemical impedance spectroscopy (EIS) tests. Also microhardness tests were performed on the substrates and on the coatings. The microstructure of the coatings was strongly influenced by the silicon distribution. In particular, a non-uniform distribution of silicon and the presence of iron-rich intermetallic (obtained in the as-cast and solution treated samples) induced the formation of more porous and thinner coatings in comparison with the ones obtained in the as printed and annealed samples. The not-uniform silicon distribution produced a not-homogenous distribution of silicon into the coatings. The particular cellular structure of the as printed sample induced the formation of a coating with a higher amorphous fraction, in comparison with the ones produced on the other samples. The higher thickness and lower porosity of the coatings obtained on the annealed and as printed samples resulted in an increase of the corrosion resistance
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
Variations 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
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
Corrosion resistance and surface characteristics of plasma electrolytic oxidation coating produced on steels
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Structural characterization and electrocatalytic properties of Au30Zr70 amorphous alloy obtained by rapid quenching
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