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Spark Plasma Sintering Processing for the Evaluation of Cryomilled CoNiCrAlY Alloys for High Temperature Applications in Oxidizing Environment
No full textThe aim of this work is to investigate the use of Spark Plasma Sintering (SPS) as a rapid and efficient approach to evaluate possible benefits deriving from cryogenic mechano-treatments of MCrAlY systems for high temperature applications in oxidizing conditions. Specifically, following our previous investigation, the influence of cryomilling on Co–32Ni–21Cr–8Al–0.5Y (wt.%) alloy characteristics is systematically analyzed in this work.
It is shown that mechanical milling in liquid N2 produces morphology changes, particle size increase, crystallite size decrease down to nanometric level (about 20 nm sized) and the formation of oxide nanodispersoids in the processed powders. These features are found to be responsible for the significant influence of the cryogenic treatment on the sintering behavior of resulting powders. Specifically, the densification process is progressively favoured if cryomilling intensity does not exceed a certain level. In contrast, powders sintering becomes relatively more difficult with severely milled powders. It is shown that a significant microstructure refinement (down to 350 ± 150 grain sized) is obtained in SPSed samples prepared from cryomilled powders. When cryomilled CoNiCrAlY SPSed specimens are exposed to an oxidizing environment at 1100 °C, an α-Al2O3 layer tends to be selectively produced on their external surface, thus limiting the formation of less protective mixed oxides observed when the unmilled system is oxidized under the same condition. Al depletion from the bulk of the sample is correspondingly reduced. Therefore, the obtained results provide a useful contribution for the identification of the optimal cryomilling conditions leading to high-temperature oxidation resistance improvement in thermal barrier coatings of gas turbine engines
Spark plasma sintering of cryomilled CoNiCrAlY powders
No full textThe influence of a cryomilling treatment in liquid N2 on the characteristics of Co-32Ni-21Cr-8Al-0.5Y powders is first investigated in this work. The cryogenic process is then followed by a consolidation step performed using Spark Plasma Sintering. Different morphology, particle size increase, crystallite size decrease down to nanometric level and higher sinterability are the most important changes observed in CoNiCrAlY powders after cryomilling. Correspondingly, a relatively finer micro structure is obtained in SPSed samples. Moreover, if samples obtained starting from cryomilled powders are exposed to an oxidizing environment at high temperature, a protective a-Al203 layer is produced on their external surface, while the formation of undesired unstable oxides is hindered. This result seems promising with the final aim of increasing high-temperature oxidation resistance in TBC of gas turbine engines
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
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