1,720,955 research outputs found
Ricoprimento di manufatti Laser-Powder Bed Fusion (L-PBF) tramite termospruzzatura High Velocity Oxygen-Fuel (HVOF)
No full textA partire dal decennio scorso, le tecnologie additive hanno iniziato ad acquisire sempre più importanza nella produzione industriale globale. Tra queste, la tecnologia Laser-Powder Bed Fusion (L-PBF) si è così diffusa da avere sostituito le tecnologie tradizionali nella produzione di alcuni componenti metallici. Molti di questi componenti operano in ambienti corrosivi o sono coinvolti in contatti tribologici; pertanto, devono spesso essere rivestiti o sottoposti a trattamenti superficiali. Nella scelta dei trattamenti e dei rivestimenti da applicare, occorre considerare le caratteristiche peculiari dei componenti L-PBF, prima fra tutte, l’elevata rugosità che ne caratterizza le superfici. Tale caratteristica è spesso considerata una limitazione, in quanto inficia la resistenza a fatica dei componenti e compromette l’applicazione di alcuni rivestimenti. Tuttavia, essa può rappresentare un’opportunità nella deposizione di rivestimenti termospruzzati, che necessitano di substrati con una moderata rugosità, al fine di aderire adeguatamente. Le superfici L-PBF potrebbero accogliere questi rivestimenti senza necessità di lavorazioni intermedie. In questo lavoro, sono stati depositati dei rivestimenti termospruzzati a base WC-10%Co4%Cr ottenuti via High Velocity Oxygen-Fuel (HVOF) su substrati in acciaio AISI 316L, realizzati mediante L-PBF. Per studiare l’influenza della morfologia superficiale del substrato sull’adesione e sulla resistenza a corrosione dei rivestimenti, essi sono stati depositati su: superfici “as built” ottenute con due diversi set di parametri di costruzione, superfici sabbiate, e superfici sottoposte a due diversi trattamenti di rifusione laser. È stata anche valutata l’eventuale influenza della direzione di crescita delle superfici L-PBF: parallela, perpendicolare, o inclinata rispetto alla piattaforma di costruzione. Per indagare gli effetti della possibile presenza di strati di ossido superficiali, inoltre, alcuni substrati sono stati sottoposti a decapaggio chimico. Come riferimento, i rivestimenti sono stati depositati su tradizionali componenti massivi in acciaio inossidabile, preventivamente sabbiati. Su ogni superficie, indipendentemente dalla morfologia e dai trattamenti eseguiti, sono stati ottenuti rivestimenti densi. La bassa porosità dei rivestimenti è stata confermata dai test di corrosione elettrochimica, che hanno mostrato un andamento confrontabile per i campioni L-PBF e per quelli di riferimento. I test di adesione a trazione hanno restituito risultati soddisfacenti; generalmente, la forza di adesione dei rivestimenti sulle superfici L-PBF è risultata paragonabile a quella misurata sui riferimenti. Tali risultati sono stati confermati dai test di impatto ciclico, a seguito dei quali non sono stati osservati fenomeni di distacco o delaminazione dei rivestimenti. Il decapaggio chimico si è rivelato particolarmente vantaggioso in termini di adesione. Sia nei test di impatto, sia nei test di adesione a trazione, i campioni decapati hanno generalmente mostrato le migliori prestazioni. Superfici così trattate, infatti, non solo garantiscono l’aggancio meccanico del rivestimento al substrato, ma consentono la diffusione degli elementi del rivestimento nel metallo sottostante. I componenti realizzati mediante L-PBF, dunque, sembrano poter accogliere la deposizione di rivestimenti termospruzzati senza richiedere operazioni di finitura superficiale intermedie. La rimozione degli ossidi superficiali mediante un trattamento di decapaggio potrebbe essere l’unica operazione necessaria, al fine di migliorare ulteriormente l’adesione dei rivestimenti.Since the 2010s, additive manufacturing technologies have increasingly gained more importance in global industrial production. Among these, Laser-Powder Bed Fusion (L-PBF) stands out as the most widely used method, gradually replacing conventional subtractive techniques to produce diverse metallic parts. Many of these components are subjected to tribological contacts and corrosive environments. Therefore, they need surface treatments or coatings. When choosing a treatment or coating, the unique properties of L-PBF parts, such as their relatively high roughness, must be considered. While high roughness is typically seen as a limitation, as it affects the fatigue resistance of components, and it poses challenges for the application of certain coatings, it could represent an opportunity in the deposition of thermal spray coatings. Indeed, these coatings require substrates with moderate roughness to ensure proper adhesion. The roughness of L-PBF surfaces could remove the need for intermediate finishing treatments, simplifying the coating application process. In this work, we deposited WC-10%Co4%Cr-based coatings by means of High Velocity Oxygen-Fuel (HVOF) onto AISI 316L L-PBF substrates, with different surface conditions. To evaluate the influence of the substrate surface morphology, we employed as-built surfaces obtained with two different sets of building parameters, sandblasted surfaces, and laser-remelted ones. We also examined L-PBF surfaces grown along different directions: parallel, perpendicular, or inclined with respect to the build platform. Furthermore, to investigate the effects of the presence of surface oxide layers, some substrates were subjected to chemical pickling. As a benchmark, we deposited the coatings on a grit-blasted stainless-steel bulk. Dense coatings were obtained on all surfaces, regardless their morphology and the applied treatments. Electrochemical corrosion tests confirmed the low porosity of the coatings, with comparable results obtained with both the L-PBF and reference samples. The tensile adhesion tests produced satisfactory results: the adhesion strength of coatings on L-PBF surfaces was generally comparable to that observed on the reference samples. These findings were further validated through cyclic impact tests, where no detachment or delamination phenomena were observed. Notably, pickling demonstrated significant advantages in terms of adhesion. Indeed, in both impact and tensile adhesion tests, the pickled samples exhibited excellent performance. Surfaces in pickled conditions not only guarantee the mechanical bonding of the coating to the substrate but also facilitate diffusion bonding between the molten splats and the clean metal. L-PBF parts, therefore, seem to be able to accommodate the deposition of thermal spray coatings without requiring intermediate surface finishing treatments. The removal of surface oxides through a pickling treatment could be the only operation needed to attain the best coating/substrate adhesion
Deposition of high-velocity oxygen-fuel (HVOF) coatings on laser-powder bed fused (L-PBF) parts subjected to in-situ laser remelting treatments
Get PDFIn this work, we focused on enhancing the adhesion between High Velocity Oxygen-Fuel (HVOF) sprayed coatings and Laser-Powder Bed Fused (L-PBF) substrates by modifying the substrate surface through in-situ laser remelting treatments. Additionally, we investigated whether deposition on laser-treated substrates affected the coating microstructure and performance. Therefore, WC-10%Co-4%Cr coatings were deposited on AISI 316 L stainless steel substrates in as-built conditions and after two different in-situ laser remelting treatments. All substrates were coated both before and after a pickling treatment. Grit-blasted bulk stainless steel samples served as references. Laser remelting changed the morphology of the L-PBF surfaces depending on the laser parameters used. The most energetic treatment resulted in more widely spaced grooves and melted the unmelted spherical particles attached to the as-built surface, leading to a more uniform material distribution. These changes influenced the adhesion-cohesion of the coatings. Although all tensile test failures were primarily cohesive, the coatings deposited on the substrates subjected to the most energetic treatment exhibited an increased adhesion-cohesion strength, exceeding 80 MPa, while all other samples showed values around 70 MPa. When the substrate was subjected to remelting treatments, however, the corrosion resistance of the coated systems decreased due to faster substrate corrosion in areas exposed to corrosive agents penetrating through coating defects
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
Pre-treatment of Selective Laser Melting (SLM) surfaces for thermal spray coating
No full textIn this work, we investigated the deposition of thermal spray coatings onto additively manufactured parts obtained by Selective Laser Melting (SLM). SLM is indeed replacing conventional subtractive machining to produce diverse industrial parts; hence, it will become increasingly frequent to apply thermal spray coatings onto SLM surfaces. Whilst grit-blasting is the most widely accepted process to prepare a conventionally machined part for a thermal spray coating, the unique surface texture of SLM surfaces might open new possibilities. As a case study, we chose High Velocity Oxygen-Fuel (HVOF) spraying of WC-10%Co4%Cr onto AISI 316 L SLM surfaces in three different conditions: “as built”, pickled, or grit-blasted. We also examined SLM surfaces grown along different directions: parallel, perpendicular, or inclined with respect to the build platform. The references were a machined and grit-blasted SLM part, and a grit-blasted stainless steel bulk.
Dense coatings were obtained on every surface regardless of its roughness and pre-treatment. Electrochemical corrosion testing confirmed the low porosity of the layers. Tensile adhesion/cohesion strength was >70 MPa on both SLM and reference surfaces, but the presence of an oxide scale on as-built surfaces degraded the adhesion strength to some extent. Although TEM analysis showed occasional evidence of diffusion bonding between the coating and the oxide scale, cyclic impact tests revealed that the scale itself broke.
Particularly strong adhesion was achieved with pickled surfaces; indeed, failure was only cohesive (i.e. within the coating) in both tensile and impact tests. In addition to mechanical interlocking to the rough surface profile, TEM showed widespread diffusion bonding to the clean metal. An SLM part might therefore need chemical activation but no subtractive machining before application of a thermal spray coating. The coating also exerts a levelling action toward the SLM surface, i.e. the coated surface is smoother than the as built one
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
- …
