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Alloying of high purity copper surfaces with cathodic arc aluminum plasma
Get PDFAl-Cu sistemi uzunca bir süredir bilimsel ve teknolojik alanda ilgi odağı olmuştur. Özellikle bakırca zengin aluminyum alaşımları yüksek elektrik ve termal iletkenlikleri ve kolay şekil verilebilir olmalarından dolayı yaygın bir şekilde mühendislik malzemesi olarak kullanılmaktadırlar. Buna ek olarak, Al-Cu faz diagramının bakırca zengin kısmında yer alan aluminyum bronzları mekanik ve fiziksel özelliklerinden dolayı ilgi çekicidirler. Kompozisyonları ağırlıkça %5-%11 arasında aluminyum içeren aluminyum bronzları yüksek mukavemet, sertlik, aşınma dayanımı ve korozyon direncine sahip olmalarından dolayı endüstride yaygın olarak kullanılmaktadırlar. Çeşitli taban malzemelerin yüzeylerinde aluminyum bronz tabakası oluşturmak amacıyla bir takım fiziksel buhar biriktirme teknikleri kullanılmıştır. Bu tekniklerin hemen hemen tamamında, kaplama işleminden sonra, istenilen yapının elde edilmesi için değişik sıcaklık ve sürelerde ısıl işlemlerin yapılması gerekmektedir. Bu çalışmada, katodik ark fiziksel buhar biriktirme (KA-FBB) yöntemi ile yüksek saflıktaki bakır taban malzemesinin yüzeyinin herhangi bir ısıl işleme gerek duyulmadan alaşımlandırılması hedeflenmiştir. KA-FBB deneyleri sırasında aluminyum katod kullanılmış ve taban malzemeye sırasıyla -150 V (kaplama) ve -1000 V (yayındırma) bias voltajı uygulanmıştır. KA-FBB işlemi sırasında uygulanan kaplama ve yayındırma basamaklarının yüzey mikroyapısı üzerindeki etkileri, x ışınları kırınım (XRD) ve taramalı elektron mikroskobu (SEM) çalışmaları ile incelenmiştir. Yapılan deneyler sonucunda yüksek saflıktaki bakır taban malzemenin yüzeyinde ağırlıklı olarak martensitik yapıda β1-AlCu3 yapısı ve (Cu) katı çözeltisi oluşmuştur. Bu fazlara ek olarak, modifiye edilmiş yüzeyde az miktarda γ1-Al4Cu9 intermetalik yapısının da varlığı tespit edilmiştir. Anahtar Kelimeler: Katodik ark fiziksel buhar biriktirme, yüzey modifikasyonu, Al-Cu sistemi, aluminyum bronzları, intermetalik.The Al-Cu system has been a focus of scientific and technological interest over decades. The system is theoretically interesting because of its unresolved phases (Dong et al., 2000; Gulay and Harbrecht, 2004; Liu et al., 1998; Hannech et al., 2003) microstructural characteristics depending on cooling rates (Eskin et al., 2005) and applied magnetic and electrical fields during solidification (Liu et al., 2004; Li et al., 2006), martensitic and massive transformations (Murray, 1985) and metastable Guinier Preston zones (Lochte et al., 1980; Lokker et al., 2001). Al-Cu alloys are used as interconnects in integrated circuits because of their high conductivity and their acceptable processing properties (Lokker et al., 2001) and they could be employed in semi-conductor devices (Ene et al., 2007). Cu-based aluminum alloys are used as engineering materials because of their high electrical and thermal conductivity and easy formability. Considering the copper rich side of Al-Cu phase diagram, aluminum bronze and γ1-Al4Cu9 structures are interesting due to their mechanical and physical properties. A variety of aluminium bronzes of differing compositions ranging from 5% to 11% aluminium by weight have been used in industry for their high strength, high hardness, wear resistance, corrosion resistance and biostatic effects (Alam et al., 2001). The intermetallic compound γ1-Al4Cu9 is reported as one of the hardest and strongest intermetallic compounds in Al-Cu binary system (Rabkin et al., 1970). In addition, low electrical resistivity of γ1-Al4Cu9 intermetallic phase could make them suitable for metallization material application for large scale integration (LSI) technology (Atsushi and Sasaki, 1991). Al-Cu is a complex system which contains many phases and invariant transformations, most of which exists in the Cu-rich side of the binary phase diagram (Murray, 1985). The phase relations of the system are not yet completely clarified and the structures of some high temperature phases are still unresolved (Hannech et al., 2003; Gulay and Harbrecht, 2004). Cu-rich side of the Al-Cu phase diagram involves a eutectoid reaction through which β-AlCu3 phase transforms into α-Cu solid solution and γ-Al4Cu9 at ~567°C. β-AlCu3 phase can also be retained metastably due to the sluggishness of the eutectoid reaction and several metastable reactions such as β→ β1+(Cu) are also present in that region of the phase diagram (Murray, 1985). Aluminum bronze structures have been obtained on the surfaces of various substrates by PVD (Liang et al., 2000) arc spraying (Zhang et al., 2006), thermal spraying (Barik et al., 2005), low pressure plasma spraying (Alam et al., 2001) and laser surface alloying (Tang et al., 2006). In addition, numerous studies about PVD processes that used layered growth and annealing for alloying of the surfaces, have been published (Kanjilal et al., 2002; Cekada et al., 2004). Recently, a cathodic arc physical vapour deposition (CAPVD) technique has been introduced, based on sequential deposition (at low bias voltages) and bombardment (at high bias voltages) of the selected target material on the surface of the substrate (Şireli, 2005; Çorlu and Ürgen, 2009). It was proposed that, surface heating and momentum transfer effects created during energetic metal ion bombardment and the defective structure of the deposits resulted in alloying of the surfaces and formation of intermetallics at the surface. In this study, we aimed to modify the surfaces of copper substrates in order to obtain aluminum bronze (>70 at.% Cu) structures at the surfaces of the substrates by using the CAPVD technique. Surface alloying and intermetallic formation was realized by sequential deposition and bombardment of aluminum on surfaces of copper substrates. The effects of the duration of the deposition- bombardment stages of the process on the structure and chemistry of the treated surfaces were investigated with XRD and SEM. XRD patterns showed that the modified zone mainly consisted of a mixture of martensitic β1-AlCu3 and (Cu) solid solution, which was accompanied by γ1-Al4Cu9 intermetallic phase. For a detailed microstructural analysis, the cross-sectional samples were etched with FeCl3 solution in order to dissolve the (Cu) phase and reveal the β-AlCu3 phase. According to SEM investigations after etching with FeCl3 solution, modified zone, with a thickness of ~15µm, consisted of three phases, which corresponded to (Cu) solid solution, β1-AlCu3 phase and γ1-Al4Cu9 intermetallic phase. Keywords: Cathodic arc physical vapor deposition, surface modification, Al-Cu binary system, aluminum bronzes, intermetallics
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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