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  • 1
    Publication Date: 2017-01-01
    Print ISSN: 0925-8388
    Electronic ISSN: 1873-4669
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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  • 2
    Publication Date: 2021-03-01
    Description: In this work, weldability and hot cracking susceptibility of five alloy 718 investment castings in laser beam welding (LBW) were investigated. Influence of chemical composition, with varying Si contents from 0.05 to 0.17 wt %, solidification rate, and pre-weld heat treatment were studied by carrying out three different weldability tests, i.e., hot ductility, Varestraint, and bead-on-plate tests, after hot isostatic pressing (HIP) and solution annealing treatment. Onset of hot ductility drop was directly related to the presence of residual Laves phase, whereas the hot ductility recovery behaviour was connected to the Si content and γ grain size. LBW Varestraint tests gave rise to enhanced fusion zone (FZ) cracking with much more reduced heat-affected zone (HAZ) cracking that was mostly independent of Si content and residual Laves phase. Microstructural characterisation of bead-on-plate welding samples showed that HAZ cracking susceptibility was closely related to welding morphology. Multiple HAZ cracks were detected in nail or mushroom welding shapes, typical in keyhole mode LBW, irrespective of the chemical composition and thermal story of castings. In all LBW welds, Laves phase with a composition similar to the eutectic of the pseudo-binary equilibrium diagram of alloy 718 was formed in the FZ. The composition of this regenerated Laves phase matched with the continuous Laves phase film observed along HAZ cracks. This was strong evidence of backfilling mechanism, which is described as wetting and infiltration of terminal liquid along γ grain boundaries of parent material. The current results suggest that this cracking mechanism was activated in three-point intersections resulting from perpendicular crossing of columnar grain boundaries with fusion line and was enhanced by nail or mushroom weld shapes and narrow and columnar γ grain characteristics of castings. Neither Varestraint nor hot ductility weldability tests can reproduce this particular cracking mechanism.
    Electronic ISSN: 2075-4701
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    Publication Date: 2024-04-08
    Description: Hay momentos en que la palabra no alcanza, no contiene, no hace falta, porque el silencio grita, aúlla, acompaña y entibia. Momentos en que los sentires se hacen música y poesía y canto, en que la austeridad ante el dolor, no es menos dolor, sino la respuesta digna ante quien te enseñó que la vida solo es viva en dignidad. Ha transcurrido casi un mes, que puede ser un día o un siglo, y aún sigue ante mis ojos la visión de un pueblo, una multitud, un océano de voces, que te nombran. "Fidel", dicen, y el eco va y viene en oleadas. Imposible describir el apretado aliento de esa multitud, la humedad salada de esas miles de voces, que nos están diciendo que te has multiplicado como los panes, que te has repartido entre los otros, lo que solo puede suceder cuando el amor es tan intenso que yéndote, regresas y de repente has dejado de ser ese hombre tan alto y tan fuerte para ser esos millones a los que te has entregado en cada acto de tu vida. “Yo soy Fidel" grita la multitud y el viento lleva las voces y las siembra y siguen naciendo Fideles por todas partes, y como nunca ahora, inalcanzable para el enemigo que acecha y cuyas garras no pudieron alcanzarte nunca, te conviertes en su pesadilla, algo que ni la más avanzada tecnología puede curar. Ya eres su sombra, pero además los has condenado a verte en cada uno de aquellos en que te has repartido, en cada mujer, hombre o niño, que salga de las oscuridades de la sumisión para alzarse como lo hacías tú ante cada injusticia en el mundo. Del capítulo "Yo soy Fidel", de Stella Calloni
    Keywords: Philosophy ; History ; Latin American Studies ; bic Book Industry Communication::H Humanities::HP Philosophy::HPS Social & political philosophy ; bic Book Industry Communication::H Humanities::HB History::HBJ Regional & national history::HBJK History of the Americas ; thema EDItEUR::Q Philosophy and Religion::QD Philosophy::QDT Topics in philosophy::QDTS Social and political philosophy ; thema EDItEUR::N History and Archaeology::NH History::NHK History of the Americas
    Language: Spanish
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