1,720,961 research outputs found
Design and development of Cu-based alloys for AM in the aerospace context
No full textL'abstract è presente nell'allegato / the abstract is in the attachmen
CuCrZr alloy obtained via electron-beam powder bed fusion: Microstructural insights and precipitation behaviour
Full text linkAn in-depth characterization of microstructure and mechanical properties of CuCrZr alloy processed by electron beam powder bed fusion (EB-PBF) additive manufacturing technology was performed with the aim to investigate the effect the thermal history of the material during the building process has on the properties of printed parts. Fully dense samples with a relative density up to 99.77 ± 0.04 % were successfully obtained in optimized conditions. The samples in the as-built condition exhibit an anisotropic microstructure dependent on the energetic input. An extensive microstructural transformation occurs alongside the precipitation and segregation of chromium-rich species, driven by the elevated thermal conditions during the deposition process. This unique thermal evolution can be properly investigated and exploited to eliminate the need for further post-processing heat treatments. To identify and quantify the precipitations within the microstructure, scanning and transmission electron microscopy together with electron backscattered diffraction were used
Real-time laser spot modulation in Laser Powder-Directed Energy Deposition via wobbling: A path to superior 316L stainless steel components
Full text linkAAchieving high-quality Laser Powder-Directed Energy Deposition (LP-DED) components require the precise tuning of process parameters such as laser power, scanning speed, and laser spot size. Among these, laser spot size is a particularly critical factor. The use of a large spot size led to high building rate and process efficiency at the expense of surface finish and geometrical accuracy. This investigation aimed to understand how a variable laser spot affects the thermal history of LP-DED AISI 316L stainless steel components and consequently their microstructure and mechanical properties. The study first examined the effects of the laser spot and sample geometry on the microstructural features using optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Secondly, the characterization of mechanical properties was conducted via tensile tests and the effects of the variable laser spot on ductility and on the various strengthening mechanisms were analysed. The results revealed that using a larger laser spot leads to heat accumulation, which becomes especially crucial when depositing geometries characterized by a small cross section. These findings lay the groundwork for enhancing the LP-DED process efficiency in a more viable manner taking advantage of the different solidification conditions
Directed energy deposition of 18NiM300 steel: effect of process and post processing conditions on microstructure and properties
Full text linkThis current study investigates the effect of Direct Energy Deposition (DED) process conditions on the properties and microstructure of M300 maraging steel samples. The investigation centers on two key factors: laser power and deposition environment. The microstructure of this tool steel is analyzed by computing the Primary Cellular Arm Spacing. The findings revealed a significant influence of both inert atmosphere and laser power on cooling conditions. These different cooling rates influence the phase content as demonstrated by X-Ray Diffraction and Electron Backscatter Diffraction measurements. It was demonstrated the presence of different content of residual austenite at cell boundaries. These distinct microstructural features caused variations in the hardness values of the printed samples. Furthermore, a direct aging heat treatment was implemented, that was chosen from Differential Scanning Calorimetry measurements results. This heat treatment proves effective in achieving consistent hardness increases and eliminated the differences among samples built in different process conditions. This outcome suggests the possibility of selecting the most economically viable DED parameters for optimal results
Optimization of Process Parameters for CuCrZr Alloy Manufactured by Electron Beam Powder Bed Fusion Technology
No full textThe CuCrZr alloys exhibit advantageous mechanical properties and high electrical conductivity which
make them promising for many applications in the electrical and aerospace engineering industries, e.g.
in the manufacture of vacuum electronics and fusion energy research. Unfortunately, these two
advantageous properties are in opposition to each other, i.e., the increase of hardness, is associated to
a decrease of electrical conductivity. Additive manufacturing technologies are good candidates to
balance these two aspects to achieve high performance parts. Powder-Bed-Fusion (PBF) techniques,
in fact, involve rapid heating and cooling rates which allow to obtain huge microstructural refinements,
thereby improving the mechanical properties without any significant loss in electrical conductivity. This
study concerns the process parameter optimization for CuCrZr alloys produced using Electron-Beam-
PBF technology using a trial-and-error approach. Material was characterized by porosity analysis,
tensile and electrical conductivity measurements. The effect of process parameters on microstructure
and densification behavior was also investigated
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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