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Förstå effekten av Isotermiska värmebehandlingar på mikrostrukturen av LMD-w byggt Ti-6242
No full textThe most widely used titanium alloy in the hot sections of a jet engine is Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) and with the technological advancements additive manufacturing (AM) of Ti-6242 is of great interest. Although, there is not much published related to additively manufactured Ti-6242. The project aimed to provide an experimental input for simulations of additively manufactured,laser metal deposited–wire (LMD-w) of Ti-6242. The main part of this project has been to experimentally study the effect of isothermal temperatures and holding times on the microstructural changes in as-built Ti-6242 on Ti-64 base-plate. The evaluation of micro-structural changes with isothermal temperature, holding time and cooling rates on Ti-6242 are quantified in terms of alpha laths, phase fraction by using MIPAR (image analysis software) and preliminary determine mechanical properties by performing hardness tests.The microstructures obtained through a process are highly dependent on the thermal history is it exposed to and the mechanical properties are determined by the microstructures present. In this thesis work the alpha lath thickness and the hardness of the material increases with increasing isothermal temperature. From the phase fractions obtained forthe heat treated samples an equilibrium phase diagram and a TTT diagram is plotted for as-built microstructure
Gente afuera de una choza. "6242. El Abra. Mexico" [sic]
No full textI.O. Anverso: "6242. El Abra, México". Reverso: "2". Información en el título, fecha de toma y asunto, proporcionada por Nacho Gutiérrez R., diciembre de 2009. V.F. 449880, 449881, 449882, 449883, 449931
Effects of trampling and soil compaction on the occurrence of some Plantago species in coastal sand dunes : 4A. The vegetation of two dune grasslands in relation to physical soil factors
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6242.pdf (Publisher’s version ) (Open Access
Gente afuera de una choza. "6242. El Abra. Mexico" [sic]
No full textI.O. Anverso: "6242. El Abra, México". Reverso: "2781. Información en el título, fecha de toma y asunto, proporcionada por Nacho Gutiérrez R., diciembre de 2009. V.F. 449880, 449881, 449882, 449883, 449932
LASER-POWDER BED FUSION OF Ti-6Al-2Sn-4Zr-2Mo-0.08Si (Ti-6242) ALLOY: PROCESS-MICROSTRUCTURE-PROPERTIES RELATIONSHIP
Get PDFThe current work is focused on Laser-powder bed fusion (L-PBF) of Ti-6Al-2Sn-4Zr-2Mo-0.08Si (Ti-6242) which is a near-α titanium alloy used for high-temperature applications. The fabrication of Ti-6242 is common using conventional techniques such as casting, forging, and powder metallurgy whereas the L-PBF of Ti-6242 is comparatively new. This offers the opportunity to develop the process-microstructure-property relationship of Ti-6242 fabricated through L-PBF. This includes tasks like 3D printing of Ti-6242 followed by the study of mechanical properties and the governing microstructures of as-built (AB) and after post-processing (heat treatment in this case). In the current study, the 3D printing of Ti-6242 was done by varying the volumetric energy density (E_v) from 41.67 to 66.67 J/mm3 by changing the scanning speeds. The variation in E_v results in variation in mechanical properties. Both the microstructure and defect analysis are performed. The defect characteristics are changed from keyhole to lack of fusion by varying the E_v from high to low whereas the microstructural characteristics are almost consistent. This concluded that the changes in mechanical properties of laser-powder bed fused Ti-6242 (L-PBF-Ti-6242) are defect-driven rather than microstructure-driven in the AB condition. The sample fabricated with process parameters offering the best combination of strength and ductility is selected for further studies. The systematic study of L-PBF-Ti-6242 is further proceeded by investigating the kinetics of α to β phase transformation using differential scanning calorimetry (DSC). Both non-isothermal and isothermal kinetics models are developed using the DSC results and employing the Johnson-Mehl-Avrami-Kolmogorov equation. As the AB microstructure of L-PBF-Ti-6242 consists of α’ martensite which is a brittle constituent it shows high strength and low ductility. To achieve the strength-ductility synergy, the modeled α to β phase transformation kinetics is used to design and develop two-step (solutionizing and aging) post-process heat treatment with an emphasis on preserving the unique, ultrafine, and hierarchical microstructure. The solutionized microstructure, 900°C for 10 minutes (S), has α/α’ and β phases with different dislocation densities. This condition results in the lowest strength and highest ductility, governed by the presence of the bcc phase (β), and high mean effective slip length in the α/α’ phase. The aging process, 300°C for 48 hours following the solutionizing step (STA) results in changes in dislocation substructure in the α/α’ phase which leads to an increase in strength, controlled by a reduction in mean effective slip length. The formulated two-step heat treatment leads to the best strength-ductility synergy in this study. The high-temperature mechanical property of L-PBF-Ti-6242 was investigated for AB, S, and STA conditions. In the AB condition, the LPBF-Ti-6242 shows superior strength at high temperatures in comparison with Ti-6Al-4V. In the case of L-PBF-Ti-6242, although the STA shows superior strength at room temperature, both S and STA exhibit almost similar strength at high temperatures. It is proposed that the developed heat treatment recipe attained a better combination of strength and ductility at room as well as high temperature. This justified the importance of the study of phase transformation kinetics to develop the heat treatment recipe for titanium alloys newly fabricated through L-PBF
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
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