1,720,957 research outputs found
Tribocorrosion behaviour of HVOF cermet coatings
No full textThe main purpose of this work is to analyze the degradation mechanisms induced on industrial
HVOF cermet coatings by tribocorrosion. Tribocorrosion of cermet coatings is a subject that has not
been widely analyzed in research studies: in fact, while many works dealing with wear or corrosion of
HVOF cermet coatings are published, studies relevant to the combined processes (wear and corrosion)
are relatively few.
The tribocorrosion mechanisms of the cermet coatings were studied in a sodium chloride solution
under sliding wear, trying to combine and integrate differently produced mechanical and electrochemical
damage phenomena.
Electrochemical techniques such as potentiodynamic polarization curves as well as potentiostatic
(I vs t) or galvanostatic (E vs t) methods were used in order to stimulate and to interprete tribocorrosion
degradation mechanisms.
It was shown that coating post grinding, which is a mechanical operation usually performed after
the deposition of conventional cermet coatings in order to obtain a desired roughness, could produce
structural damages, which can greatly affect the mechano-chemical behaviour of the cermet coatings.
Mainly abrasive–adhesive wear mechanisms were observed on the coating surface and sometimes,
depending on coatings mechanical properties (fracture toughness), cracks developed during wear
causing the coating continuity breaking. In the latter case, the degradation mechanism is no longer
governed only by surface tribocorrosion, but undermining corrosion can occur, greatly affecting
sample performances and promoting coating detachment.
Cr3C2–NiCr coatings, under all the selected experimental conditions, showed good barrier properties
and substrate corrosion was never observed. Moreover, when chromium was added to the metal matrix of WC–Co based systems, tribocorrosion behaviour was enhanced and the lower tribocorrosion
rates were measured.
Finally, it was shown that electrochemical techniques can be used to govern the coating corrosion
processes and to interpret the main degradation mechanisms, even though they seem not to provide a
precise quantitative analysis of tribocorrosion
Mechanical and tribocorrosion properties of HVOF sprayed WC-Co coatings
No full textHVOF technology has been proposed in recent years for the production of engineered cermet coatings suitable for the replacement of hard chromium surface treatments of mechanical components, for aeronautical and automotive applications. The aim of this study has been to compare the mechanical and tribocorrosion properties of WC-Co cermet coatings fabricated with different processing parameters, to optimise the spraying process by evaluating the dependence of the macroscopic coating properties on the spraying procedure. Barrel length, oxygen:fuel ratio and torc-1 specimen spraying distance were selected as the main variables since their influence on cooling microstructure and macroscopic properties in the absence of corrosion is already well known. WC-Co samples were subjected to 'block on ring' wear testing, carried out in an electrochemical cell, to assess wear properties in combination with a range of corrosive conditions. The results were compared to those obtained by ordinary wear testing and electrochemical characterisation. Mechanical properties of the coatings, such as microhardness, fracture toughness and coating substrate adhesion, were also measured. Tribocorrosion testing proved better able to distinguish coating properties than conventional wear tests, due to the more severe damage induced by the corrosive attack
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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