1,721,008 research outputs found
Development of PVD coatings for the field of Al alloys forming from liquid state
No full textIl lavoro di tesi ha riguardato lo sviluppo, la caratterizzazione e la realizzazione di test atti a simulare la messa in servizio di rivestimenti sottili realizzati con tecnica Physical Vapor Deposition (PVD) per lo stampaggio dell'alluminio. Nello specifico sono stati realizzati tre diversi rivestimenti con tecnica lateral rotate arc cathode (LARC®) PVD: nitruro di zircono (ZrN), nitruro di cromo (CrN) e un mutilstrato di nitruro di cromo alluminio silicio (CrAlSiN) e due rivestimenti con tecnica Reactive Magnetron Sputtering PVD: nitruro di cromo alluminio (CrAlN) e nitruro di titanio (TiAlN). La morfologia dei rivestimenti è stata analizzata attraverso l'utilizzo di microscopia elettronica a scansione (SEM) e miscoscopia a scansione si sonda (SPM), la composizione chimica è stata studiata con spettroscopia spettroscopia EDS (Energy Dispersive X-ray), mentre le proprietà meccaniche dei rivestimenti sono state analizzate con nanoindentazione e prove di adesione. Inoltre è stata realizzata un'analisi statistica sulla presenza di difetti nei rivestimenti. Per finire i rivestimenti sono stati sottoposti a un test di fatica termica che simula le condizioni operative dello stampaggio dell'alluminio, con cicliche immersione in un bagno di alluminio fuso e in un bagno termostato di acqua e liquido distaccante per un totale di 15.000 cicl
ADDITIVE MANUFACTURING OF METAL PASSIVE WAVEGUIDE COMPONENTS
No full textAdditive manufacturing (AM) allows the production of complex shape and structures without molds directly from a three-dimensional (3D) computer aided design (CAD) model. Direct Metal Laser Sintering (DMLS) is an AM technology that enables the manufacturing of 3D components from metal powders. It offers several advantages, such as the integration of RF functionalities in a single part with complex shape, minimization of mass and envelope, reduction of lead time and costs. However, the application of DMLS to the manufacturing of passive waveguide components is currenlty limited by some technological aspects. The most important factors to evaluate are roughness, accuracy, electrical conductivity and repeatability. In order to assess the impact of these parameters on the RF performance, test lines in Ka and Q-bands, and a resonant cavity in Ku/K band has been designed. Then, two different Ku/K-band filters have been designed and tested. An aluminum alloy (AlSi10Mg) and a titanium alloy (Ti6Al4V) have been used in this work, both processed via an EOSINT M270 Xtended machine
FAILURE MODES OF PVD COATINGS IN MOLTEN Al-ALLOY CONTACT
No full textThis paper deals with a study of the failure mode of thin PVD coatings in alternated contact with molten aluminum alloy. CrN and ZrN monolayer coatings deposited through cathodic arc evaporation were used. The coatings morphology was assessed by SEM and their mechanical properties evaluated by nanohardness test performed at room temperature. An experimental test rig which cyclically immerses coated steel samples in molten Al-alloy and in a cooling bath was applied. The thermal gradient from the coating to the steel core was exalted by internal cooling channels placed in the internal cavity of samples. Periodical SEM inspections were performed to assess the damaging levels introduced by the test and to study the related decrease of substrate protection capability. Descriptions and interpretations of the damages evolutions were derived. The main conclusions achieved are that both coatings suffered by the formation of corrosion pits, which were due to a corrosion attack of the steel substrate localized at coating defects sites. In particular, at pores locations the corrosion was fast, whereas at droplets sites it required a certain incubation time. Once corrosion pits were formed they exhibited an initial tendency to expand laterally, but they did rapidly stabilize in terms of lateral dimensions. Later on two different failure modes acted in ZrN and in CrN. Extended delamination due to a marked mismatch of mechanical properties between the coating and the steel substrate developed in ZrN. On the contrary, thermal cracking due to lower hardness levels developed in CrN, but with limited delamination. Accordingly the steel substrate protection capability was evaluated to be higher in CrN than in ZrN
A preliminary study on high-entropy alloys for laser powder bed process
No full textRecently, high entropy alloys (HEAs) have represented a field of intense research in metallurgy because of their unique properties such as high temperature strength and ductility. HEAs are multiple principal element systems with five or more elements in near equiatomic concentration, usually favouring the entropic stabilization of a disordered solid solution. The choice of starting element composition (low density, refractory, etc.) allows to tailor microstructures (FCC, BCC, etc.) and resultant properties. Within this research, a propaedeutic study is conducted to develop a new HEA suitable for the powder bed additive manufacturing process called selective laser melting (SLM). SLM could provide the necessary local process control and high solidification rate to turn HEAs into engineering materials. HEAs were obtained by high energy ball milling of a proper selection of pure elemental powders (Al, Ti, V, Mn, Fe, Cu, Nb). Mechanically alloyed powders were then characterized by DSC, XRD and electron microscopy
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
Investigation of the Mechanical Properties of a Carbon Fibre-Reinforced Nylon Filament for 3D Printing
Full text linkAdditive manufacturing (i.e., 3D printing) has rapidly developed in recent years. In the recent past, many researchers have highlighted the development of in-house filaments for fused filament fabrication (FFF), which can extend the corresponding field of application. Due to the limited mechanical properties and deficient functionality of printed polymer parts, there is a need to develop printable polymer composites that exhibit high performance. This study analyses the actual mechanical characteristics of parts fabricated with a low-cost printer from a carbon fibre-reinforced nylon filament. The results show that the obtained values differ considerably from the values presented in the datasheets of various filament suppliers. Moreover, the hardness and tensile strength are influenced by the building direction, the infill percentage, and the thermal stresses, whereas the resilience is affected only by the building direction. Furthermore, the relationship between the mechanical properties and the filling factor is not linear
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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