1,720,985 research outputs found
The effect of hot isostatic pressing pressure level and solution annealing cooling rate on CM247 LC nickel-based superalloy processed by laser-based powder bed fusion
Full text linkIn the present work, CM247 LC samples produced by laser-based powder bed fusion (PBF-LB) were heat treated inside a hot isostatic pressing (HIP) furnace (HIP quench treatment) at 1260 degrees C for 3 h to combine the solution annealing with the elimination of defects of the additively manufactured parts. In particular, the effects of different applied pressures (50-170 MPa) and cooling rates (from 162 to 2450 degrees C/min) on the final densification, grain coarsening, and gamma' precipitation were studied. The results were also compared to a sample heat treated in a low-pressure furnace and gas-quenched at 195 degrees C/min. The study revealed that the applied pressure has a negligible effect on densification, grain coarsening, and the size and shape of gamma', which is always irregular after solution annealing, independently from the cooling rate. For this reason, first aging was subsequently applied at 1080 degrees C for 4 h to HIP-quenched samples, revealing that this step of treatment is effectively responsible for the final cubic shape of gamma', even if a starting irregular morphology is considered. Finally, additional samples were heat treated in an air furnace and air cooled to room temperature prior to the HIP quench; this procedure allowed assessing the solutioning effectiveness of the HIP quench with coarse precipitates typical of conventional processing (e.g., investment casting). Overall, this study underscores the efficacy of the HIP quench in enhancing microstructural attributes and mitigating defects, providing valuable insights for enhancing the properties of challenging Ni-based alloys fabricated through additive manufacturing techniques
Definition of an optimal solutioning treatment for a Ni-based superalloy processed by Additive Manufacturing
No full textThe current work aims at defining an optimal recipe for the solution annealing (SA) of a high-fraction γ’ Ni-based superalloy manufactured with Laser Powder Bed Fusion process (PBF-LB/M). The studied alloy is designed for the aeronautical or energy sectors to perform above 800°C. The microstructure obtained from PBF-LB/M process (as-built state) is extremely fine with grains aligned along the building direction, due to the thermal flow during the process. Moreover, due to the fast cooling, the main reinforcing phase (γ’, a Ni3(Al,Ti) ordered L12 precipitate) cannot precipitate. SA temperatures of 1230°C, 1245°C and 1260°C were investigated to obtain the best microstructure in terms of reinforcing precipitates’ size, shape and fraction and grain size, keeping the soaking time constant (2 hours). Then, a first aging (FA) was also applied at 1095°C for 4 hours. The test plan was configured to account for industrial furnaces thermal uncertainty, introducing also higher temperatures to verify the presence of any thermal induced porosities (TIPs) or incipient melting traces. The morphology, size and volume fraction of γ’ phase were assessed and quantified using scanning electron microscopy (SEM). Light optical microscopy (LOM) was used to evaluate the grains aspect ratio and growth during S
Directed Energy Deposition of AISI 316L Stainless Steel Powder: Effect of Process Parameters
Full text linkDuring Laser Powder-Directed Energy Deposition (LP-DED), many complex phenomena occur. These phenomena, which are strictly related to the conditions used during the building process, can affect the quality of the parts in terms of microstructural features and mechanical behavior. This paper investigates the effect of building parameters on the microstructure and the tensile properties of AISI 316L stainless-steel samples produced via LP-DED. Firstly, the building parameters were selected starting from single scan tracks by studying their morphology and geometrical features. Next, 316L LP-DED bulk samples built with two sets of parameters were characterized in terms of porosity, geometrical accuracy, microstructure, and mechanical properties. The tensile tests data were analyzed using the Voce model and a correlation between the tensile properties and the dislocation free path was found. Overall, the data indicate that porosity should not be considered the unique indicator of the quality of an LP-DED part and that a mechanical characterization should also be performed
Microstructure and Hardness Evolution of Solution Annealed Inconel 625/TiC Composite Processed by Laser Powder Bed Fusion
Full text linkThis study deals with the Inconel 625 (IN625) alloy reinforced with micro-TiC particles processed by laser powder bed fusion. The microstructure and hardness in the as-built and solution-annealed states were investigated. The microstructures of the as-built IN625 and IN625/TiC states were primarily made up of columnar grains along the building direction. After the solution annealing at 1150 °C for 2 h, the IN625 alloy consisted of equiaxed grains due to recrystallization and grain growth. On the contrary, the solution-annealed IN625/TiC composite still presented columnar grains. Therefore, the TiC particles hinder the recrystallization, indicating higher microstructure stability for the composite. For the IN625/TiC composite, both the reduced alteration of the grains and the more intensive formation of carbides prevent a remarkable hardness reduction in the solution-annealed state
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
- …
