1,727,832 research outputs found
Avaliação eletroquimica da resistencia a corrosão do aço ABNT 4140 nitretado por plasma
Get PDFDissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas.A corrosão de materiais metálicos representa um dos maiores problemas do mundo moderno. Atualmente vários são os processos utilizados para proteger os metais da corrosão e dentre eles vem despertando muito interesse a nitretação, pois representa proporciona resistência a corrosão a aços comuns, além de melhorar suas propriedades mecânicas. Neste trabalho, amostras de aço ABNT 4140 foram tratadas segundo dois parâmetros térmicos e posteriormente nitretadas em plasma com mistura de 75% de N2 e 25% de H2. Os parâmetros de tratamento térmico compreendem uma temperatura a 850oC seguindo por um revenido a 600oC durante duas horas e um recozimento a 900oC durante duas horas. As amostras, após nitretação foram resfriadas a partir de 540oC na mistura nitretante e na atmosfera ambiente, compreendendo dois parâmetros de resfriamento. O comportamento da corrosão foi avaliado em NaCl (3%) indicando a presença de baixa corrente de dissociação anódica, 1mA/cm2 para aços nitretados com espessuras de camada maiores do que 5m comparado com correntes de 105mA/cm2 para aços não tratados. Resultados das amostras oxidadas durante o ciclo de resfriamento mostraram uma melhoria na resistência a corrosão. O potencial para o processo de iniciação de pites e sua propagação bem como os de proteção de pites foram determinados em ambientes de cloreto
4140 steel in seawater
No full textCrN, TiN and AlTiN coatings were applied by the Physical Vapour Deposition (PVD) method on AISI 4140 and plasma nitrided (PN) AISI 4140 steel. The study aimed to investigate the effect of plasma nitriding before PVD on the corrosion and tribocorrosion behaviour of AISI 4140 steel in seawater. The electrochemical corrosion behaviour of the samples was evaluated in natural seawater by the potentiodynamic polarisation method. Tribocorrosion tests were performed against alumina in natural seawater under 5 N load and open circuit potential (OCP) using a ball-on-disk tribometer coupled with an electrochemical cell. As a result of the study, plasma nitriding applied before the coating significantly improved corrosion and tribocorrosion resistance of PVD CrN, TiN and AlTiN coatings. Besides, it was concluded that duplex treated low alloy AISI 4140 steel could be a candidate instead of stainless steel in tribocorrosion conditions for the marine environment.Bartin Universitesi [2017-FEN CD-02]Bartin Universitesi, Grant/Award Number: 2017-FEN CD-0
Search for the y(4140) via e(+)e(-) -> gamma phi J/psi at root s=4.23, 4.26 and 4.36 Gev
No full textÇetin, Serkant Ali (Dogus Author)Using data samples collected at center-of-mass energies root s = 4.23, 4.26, and 4.36 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the production of the charmoniumlike state Y(4140) through a radiative transition followed by its decay to phi J/psi. No significant signal is observed and upper limits on sigma[e(+)e(-) -> gamma Y(4140)] . B(Y(4140) -> phi J/psi at the 90% confidence level are estimated as 0.35, 0.28, and 0.33 pb at root s = 4.23, 4.26, and 4.36 GeV, respectively
Exploring the resonances X(4140) and X(4274) through their decay channels
Get PDFAzizi, Kazem (Doğuş Author)Investigation of the resonances X(4140) and X(4274), which were recently confirmed by the LHCb Collaboration [1], is carried out by treating them as the color triplet and sextet [cs] [(c) over bar (s) over bar] diquark-antidiquark states with the spin-parity J(P) = 1(+), respectively. We calculate the masses and meson-current couplings of these tetraquarks in the context of the QCD two-point sum rule method by taking into account the quark, gluon, and mixed vacuum condensates up to eight dimensions. We also study the vertices X(4140)J/psi phi and X(4274)J/psi phi and evaluate corresponding strong couplings g(X(4140)J/psi phi) and g(X(4274)J/psi phi) by means of the QCD light-cone sum rule method and a technique of the soft-meson approximation. In turn, these couplings contain required information to determine the width of the X(4140) -> J/psi phi and X(4274) -> J/psi phi decay channels. We compare our results for the masses and decay widths of the X(4140) and X(4274) resonances with the LHCb data and alternative theoretical predictions
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
ASISI 4140 çeliğinin sıcak dövme karakteristiğinin incelenmesi
No full text06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Endüstride sıcak dövme işlemi ile AISI 4140 çeliğinden üretilen parçalar yaygın bir şekilde kullanılmaktadır. Buna rağmen endüstride AISI 4140 çeliğinin sıcak dövme çalışmasıyla ile ilgili yazılı doküman sınırlı sayıdadır. Bu çalışmada AISI 4140 çeliğin sıcak dövme sonrası farklı ostenitleme ve menevişleme sıcaklıkları sonucunda malzemedeki mekanik ve mikro yapısal değişimler deneysel olarak incelenmiştir. Endüstriyel olarak üretilen parçalardan elde edilen numuneler 900°C, 880°C ve 860°C sıcaklıklarda ostenitlenip yağda su verildikten sonra 640°C, 570°C ve 480°C sıcaklıklarda menevişlenmişlerdir. Tüm numunelerde ostenitleme süresi 140 dakika, menevişleme süresi de 200 dakika olarak belirlenmiştir. Bu numunelerin sertlik ve çekme testleri ile XRD ve metalografik mikroyapı analizleri yapılmıştır. Yapılan ısıl işlemler sonucunda bu numuneler TS EN ISO 6892-1 göre çekme, TS EN ISO 6506 -1 göre de sertlik testine tabi tutulmuş ve mikro yapıları optik mikroskop ve SEM'de incelenmiştir. SEM incelemesi sonucunda yapıda farklılıklar görülen bölgelerden EDS analizi alınarak sonuçlar değerlendirilmiştir. Yapıda oluşabilecek fazları belirlemek için XRD analizi yapılmıştır. Ostenitleme ve menevişleme sıcaklıkları sabit tutularak, AISI 4140 çeliğinin sıcak dövme sonrasındaki ısıl işleminde ostenitleme ve menevişleme sıcaklıklarının mekanik ve mikroyapı özelliklerine etkisi tespit edilmiş ve aralarındaki farklar incelenmiştir.Parts that are produced from AISI 4140 steel using hot-forging process are widely used in industry. Nevertheless, there are few written documents related to hot-forging of AISI 4140 steel. In this study, following the hotforging process, mechanical and microstructural changes at different austenitizing and tempering temperatures have been analyzed experimentally. Samples that are obtained from industrially produced parts have been austenitized at 900°C, 880°C and 860°C then quenched with oil and tempered at 640°C, 570°C and 480°C. Austenitizing duration for all the samples has been 140 minutes and tempering time has been 200 minutes. Hardness and Tensile tests along with XRD and metallographic microstructure analyses of these samples have been performed. Following the Heat-Treatment performed, these samples have been subjected to tensile testing in acc. with TS EN ISO 6892-1 and hardness testing in acc. with TS EN ISO 6506-1. In consequence of SEM examination, EDS analysis has been performed on areas showing differences in micro-structure. XRD analysis has been performed in order to determine the phases that may occur. After the heat treatment of hot forged AISI 4140 steel, keeping the austenitization and tempering temperatures constant, the effect of these temperature on mechanical and microstructural properties has been investigated
Investigation on wear mechanisms of boronized AISI 4140 steel
No full textIn this study, AISI 4140 steel was subjected to box boronizing treatment at 1123 K, 1173 K and 1223 K for 2h, 4h, and 6h with commercially EKabor 2 powders. Friction and wear behaviour of the boronized and following worn AISI 4140 have been examined. After the wear tests, surface profilometer image analysis and EDS analysis were done. Also wear track area, wear track volume and wear rate were calculated based on the surface of the worn materials. In the AISI 4140 steel and in the boronized samples for 2 h severely plastic deformation wear mechanism were determined whereas in the samples boronized for 4h and 6h micro-ploughing wear mechanism were determined. Properties of boride layers have an effect on the type of wear mechanism. The boronized samples showed up to 27.3 times higher wear resistance than non-boronized AISI 4140 steel. © 2017, Scibulcom Ltd. All rights reserved.Karabük University Research Council, (14/1-YL-016
Oddball Y(4140) as the molecular cousin of Y(3930)
No full textIn my talk, we present the dynamical study of Y(4140) and Y(3930) under the D-s*(D) over bar (s)* and D*(D) over bar* molecular assignments respectively The importance to theoretically and experimentally study their open-charm decay, hidden-charm decay, radiative decay and double-photon decay is proposed combing with the theoretical calculation of the decay behavior of Y(4140) and Y(3930) According to the recent new experimental progress made by Belle, we further indicate the reasonability of molecular explanation to Y(4140) Another event cluster around 4270 MeV in the J/psi Phi invariant mass spectrum of B -> KJ/psi Phi can provide us more hints to reveal the creation mechanism of molecular structure in B meson decay, which will be helpful to clarify the underlying structure of Y(4140) and Y(3930
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