1,720,967 research outputs found
Aging Behaviour of a 12.2Cr-10Ni-1Mo-1Ti-0.6Al Precipitation-Hardening Stainless Steel Manufactured via Laser Powder Bed Fusion
Full text linkThe combination of precipitation-hardening stainless steels (PH-SS) and laser powder bed fusion (LPBF) enables the manufacturing of tools for plastic injection moulding with optimised geometry and conformal cooling channels, with potential benefits in terms of productivity, part quality, and tool duration. Moreover, the suitability of LPBF-manufactured PH-SS in the as-built (AB) condition to be age-hardened through a direct aging (DA) treatment enables a great heat treatment simplification with respect to the traditional solution annealing and aging treatment (SA). However, plastic injection moulding tools experience severe thermal cycles during their service, which can lead to over-aging of PH-SS and thus shorten tool life. Therefore, proper thermal stability is required to ensure adequate tool life and reliability. The aim of the present work is to investigate the aging and over-aging behaviour of a commercially available PH-SS (AMPO M789) manufactured by LPBF in the AB condition and after a solution-annealing treatment in order to evaluate the effect of the heat treatment condition on the microstructure and the aging and over-aging response, aiming at assessing its feasibility for plastic injection moulding applications. The AB microstructure features melt pool borders, oriented martensite grains, and a cellular solidification sub-structure, and was retained during aging and over-aging. On the other hand, a homogeneous and isotropic martensite structure was present after solution annealing and quenching, with no melt pool borders, cellular structure, or oriented grains. The results indicate no significant difference between AB and solution-annealed and quenched specimens in terms of aging and over-aging behaviour and peak hardness (in the range 580–600 HV), despite the considerably different microstructures. Over-aging was attributed to both the coarsening of strengthening precipitates and martensite-to-austenite reversion (up to ~11 vol.%) upon prolonged exposure to high temperature. Based on the results, guidelines to aid the selection of the most suitable heat treatment procedure are proposed
Effect of heat treatment on microstructure and mechanical properties of a Fe-12.2Cr-10Ni-1Mo-1Ti-0.6Al precipitation hardening-stainless steel manufactured via laser powder bed fusion
No full textPrecipitation hardening-stainless steels (PH-SS) can be easily manufactured by laser powder bed fusion (LPBF) and hardened to high strength, enabling the production of molds and dies featuring conformal cooling channels with no cracks, high strength, and corrosion resistance. Previous works showed that LPBF-manufactured PH-SS can be strengthened through a one-step direct aging (DA) treatment, instead of the traditional solution annealing and aging (SA), with cost, time, and energy consumption reduction. However, significant differences remain between the microstructures of DA- and SA-treated parts, potentially affecting the resulting mechanical behavior. The present work investigates the microstructure and the mechanical behavior of a PH-SS manufactured by LPBF, AMPO M789, in the as-built (AB) condition and after SA and DA heat treatments. Compared to the AB state, both heat treatments led to a great increment of hardness (from ~ 320 HV to 570–585 HV), yield strength (152–164%) and tensile strength (76–84%) together with a reduction of ductility (31–46%) and impact toughness (93–95%). However, DA led to significantly higher ductility (+ 29%) and toughness (+ 25%) than SA despite a strength reduction of only 5% and a similar hardness. The better strength–ductility balance of DA was attributed to a higher austenite content (~ 8% vs. ~ 3%) and to the oriented microstructure resulting from LPBF, retained by DA and recovered by SA, which limited the cleavage fracture mode thus promoting a ductile behavior. Results indicated the feasibility of DA to replace SA for LPBF-manufactured PH-SS in industrial applications
Laser-directed energy deposition additive manufacturing of a lean hot work tool steel: Tempering behavior and impact toughness
No full textHWTS 50 is a Cr, Mo, V is a new lean hot work tool steel with ∼0.2 wt% carbon, designed with chemical composition modifications to achieve comparable properties and temper resistance to those of medium carbon hot work tool steels such as AISI H13 (∼0.4 % C in wt.), while offering improved processability in laser additive manufacturing (LAM) processes. This paper reports on the processing and properties of this tool steel by laser-directed energy deposition (L-DED). Results suggest achievement of near-fully dense and crack-free martensitic microstructure with up to 6 vol% retained austenite (RA), which is substantially lower than that typically found in laser AM-processed AISI H13 (i.e., up to 20 vol%). As-built (AB) material exhibits a hardness of ∼47 HRC and Charpy V-notch impact energy of ∼20 J. Hardness of 48–50 HRC can be achieved by tempering slightly above the secondary hardness peak of 575 °C, either through quenching and tempering or direct double tempering from AB condition. Direct tempering improves temper resistance due to higher dislocation density and higher matrix supersaturation in elements carbon, nitrogen, and vanadium in AB condition, leading to a higher number density of fine and stable secondary carbides through over-tempering. In the above hardness range, the impact toughness of quenched and tempered steel was substantially higher than that of directly tempered one (i.e., ∼18 J vs. ∼12 J). Increased impact energy by prior quenching could be ascribed to microstructural homogenization, removal of inter-dendritic micro-segregation, and columnar prior austenite grain boundaries, which act as preferential sites for chains of alloy carbides precipitation, serving as low energy preferential crack initiation and propagation path. The new steel grade showed enhanced tempering resistance compared to AISI H13, particularly at elevated temperatures (i.e., >600 °C). Enhanced AM processability, optimum balance of hardness-, impact toughness-, and tempering resistance suggest it can be used for the manufacturing and repair of hot work tool steels in laser AM processes
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
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
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