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Investigation and characterization of an Al-Mg-Zr-Sc alloy with reduced Sc content for laser powder bed fusion
Full text linkOnly few high strength Al alloys are processable by Laser Powder Bed Fusion due to the occurrence of hot cracks during solidification. In recent years, the addition of Zr and Sc in Al-Mg alloys revealed an effective solutions to suppress solidification cracking and improve strength. Nevertheless, since Sc is classified as a critical raw material by European Commission due to its high cost and supply risk, its content should be desiderably reduced. It is therefore necessary to focus on novel Al alloys featuring both enhanced processability and low amount of Sc. In this study, we investigated the microstructure and mechanical behavior of an Al-5.2Mg-0.8Zr-0.3Sc alloy, commercially available as m4pTM StrengthAl, produced by Laser Powder Bed Fusion. Simulations of equilibrium phase diagrams and Scheil solidification curves showed the precipitation of primary Al3Zr and Al3(Sc,Zr) in the liquid phase on cooling. These particles revealed able to act as nuclei for heterogeneous nucleation of grains, giving rise to a fine equiaxed structure which is able to suppress hot cracking and increase the processability of the Al-Mg-Zr-Sc alloy. Despite the reduced Sc content, the formation of secondary Al3(Sc,Zr) nano-phases during the annealing treatment led to a sharp increase of micro-hardness values, whereas a stress relief effect was monitored by residual stress measurements during aging. Both as-built and aged alloys show a bimodal grain size distribution and a similar crystallographic texture. Yield strength and ultimate tensile strength of 460 MPa and 485 MPa, respectively, were recorded in samples aged at 350 °C for 24 h and at 375 °C for 8 h
Microstructure and mechanical behavior of hot-work tool steels processed by Selective Laser Melting
No full textThe present study is aimed at identifying and testing high-strength alloys for tooling applications featuring suitable processability for laser-based additive manufacturing technologies. The microstructure and mechanical properties of the H11 hot-work tool steel and a leaner version of the same alloy (L-H11) processed by Selective Laser Melting were assessed as a function of specific microstructural conditions obtained by performing different heat treatments. Tempering was performed on quenched alloys or simply from as built material. The rapidly solidified microstructures revealed able to respond directly to precipitation hardening treatment without performing any prior solution annealing. The microstructure of the as-built alloys revealed characterized by α-Fe dendritic cells decorated at boundaries by C-rich γ-Fe regions. Air quenching was responsible for the transformation of the solidification cells into lath martensitic structures and for the formation of the M3C phase, which transformed into more complex carbide species on tempering. The hardness of quenched and tempered H11 steel is similar to that obtained by processing the alloy with conventional routes, and the final hardness gap between the two SLM processed H11 and L-H11 alloys treated according to optimal tempered condition was limited to 62 HV
Design of Wear-Resistant Austenitic Steels for Selective Laser Melting
Full text linkType 316L stainless steel feedstock powder was modified by alloying with powders containing carbide/boride-forming elements to create improved wear-resistant austenitic alloys that can be readily processed by Selective Laser Melting. Fe-based alloys with high C, B, V, and Nb contents were thus produced, resulting in a microstructure that consisted of austenitic grains and a significant amount of hard carbides and borides. Heat treatments were performed to modify the carbide distribution and morphology. Optimal hard-phase spheroidization was achieved by annealing the proposed alloys at 1150 °C for 1 hour followed by water quenching. The total increase in hardness of samples containing 20 pct of C/B-rich alloy powder was of 82.7 pct while the wear resistance could be increased by a factor of 6
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
Modification strategies for tool steels grades to achieve improved processability by SLM
No full textModification of chemical compositions of two popular steel grades to adapt their properties to peculiar Selective Laser Melting conditions and to expected applications in the tool and die sectors are proposed. A type 316L stainless steel was modified by blending with an atomized alloy rich in carbon, boron and in carbide/boride forming elements. A different strategy was adopted for a H11 tool steel grade that was diluted with a lower carbon alloy in order to increase processability and to reduce cracking tendency during solidification
Effect of vanadium on microstructure and wear behaviour of fe based C–B–Ni hardfacing alloy
Full text linkEffect of combined additions of Sc, Zr and Ti on hot-cracking resistance and precipitation behaviour in Al-Mg alloy by L-PBF
Full text linkThe request for high-performance aluminum components prompts research into innovative alloys compatible with laser-based additive manufacturing processes, leveraging grain refiners in their composition to mitigate hot- cracking and enhance strength. While the addition of Sc and Zr in Al-Mg alloys has been widely investigated, the high cost and supply risks associated with Sc necessitate reducing its amount and replacing, at least partially, with other inoculants. In this preliminary study, the amount of Sc replaceable with different concentrations of Zr or Ti is evaluated investigating the laser powder bed fusion processability of three powder feedstocks: a pre- alloyed Al-Mg-Zr-Sc powder, a blend of the previous alloy with addition of Zr particles, and a further blend of an alloy depleted of Zr with added Ti particles. The experimental analyses on the laser-processed alloys showed that the standard and the Zr-enriched alloys featured a bimodal microstructure free from cracks with fine equiaxed grains at the edge of the molten pools and coarser grains at their centers. In the alloy variant depleted in Zr with addition of Ti particles a columnar structure was observed and hot-cracks appeared. Thermodynamic simulations of phase formation allowed defining the precipitation kinetics during solidification and direct aging, showing increased precipitation in alloys with higher Zr content, while the presence of Ti resulted in sluggish precipitation. Experimental aging tests demonstrated significant increases in microhardness, with peak values of the modified alloys achieved after 12 h at 375 ◦ C
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
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