Current Search: Senapati, Sephalika (x)
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Title
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EVOLUTION OF LAMELLAR STRUCTURES IN AL-AG ALLOYS.
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Creator
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Senapati, Sephalika, Heinrich, Helge, University of Central Florida
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Abstract / Description
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In the present study, the formation and the evolution of lamellar structures in different Al-Ag alloys were investigated by transmission electron microscopy (TEM). Plates of the hexagonalÁ phase form semi-coherently on the {111} planes of the face centered cubic lattice of the alloy after the formation of Guinier-Preston zones. Guinier-Preston zones are metastable coherent preprecipitates which are silver rich in the aluminum-rich Al-Ag alloys. The decomposition of aluminum rich...
Show moreIn the present study, the formation and the evolution of lamellar structures in different Al-Ag alloys were investigated by transmission electron microscopy (TEM). Plates of the hexagonalÁ phase form semi-coherently on the {111} planes of the face centered cubic lattice of the alloy after the formation of Guinier-Preston zones. Guinier-Preston zones are metastable coherent preprecipitates which are silver rich in the aluminum-rich Al-Ag alloys. The decomposition of aluminum rich Al-Ag alloys, particularly the sequence of the later stages of precipitate formation was studied. With scanning electron microscopy and high-resolution transmission electron microscopy the development of the Á phase was investigated. Samples cut from different Al-Ag alloys were homogenized at temperatures between 530C to 560C to obtain a single phase f.c.c solid solution. The samples were then quenched to room temperature, followed by heat treatments at temperatures between 140C and 220C for varying lengths of times. While Guinier-Preston zones increase in diameter with increasing aging duration, silver rich platelets of the Á phase form. The Á phase is the next metastable phase in the decomposition sequence before finally the Á phase transforms to the stable silver-rich phase, termedÁ . For samples with silver contents above 12 at.% a parallel lamellar alignment of fine Á-plates and Alrich matrix is found after extended heat treatments. For all alloys with Ag concentrations below 12 at.% individual Á plates are found on all four possible (111) planes of the ¿ matrix. iv A method is presented to calibrate the medium-magnification high-angle annular dark-field contrast in scanning transmission electron microscopy. This calibration allows for the quantitative measurement of plate thicknesses from high-angle annular dark-field scanning transmission electron micrographs of Ag2Al plates inclined to the electron beam. Results from these measurements are in good agreement with direct bright-field micrographs of plates viewed edge-on.
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Date Issued
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2005
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Identifier
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CFE0000874, ucf:46648
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000874