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dc.contributor.advisorPoirier, David R.en_US
dc.contributor.authorFrueh, Christian*
dc.creatorFrueh, Christianen_US
dc.date.accessioned2013-05-09T10:39:11Z
dc.date.available2013-05-09T10:39:11Z
dc.date.issued2002en_US
dc.identifier.urihttp://hdl.handle.net/10150/289787
dc.description.abstractThis work provides evidence that channels in directionally solidified hypoeutectic Pb-Sn alloys nucleate at the dendrite tips. Using a finite-element simulator, distinctive 'convective signatures' are shown to exist for convectively unstable cases, where the instability of a system is shown to be largely a function of the thickness of an inverted density layer that exists ahead of the moving solidification front. With D the diffusion coefficient in the melt and V the solidification rate, the thickness of this layer, and therefore the stability of the systems studied, is shown to be a function of the length scale D/ V, where it is shown that channeling can be turned on or off simply by changing this length scale. This work also validates a finite element model of dendritic solidification by comparing predicted results to data resulting from eleven directionally solidified hypoeutectic Pb-Sn samples, which were produced under various thermal gradients and solidification rates. For all but one of the cases, which was thought to be borderline between channeling and not channeling, predictions of whether channel defects formed were supported by experiments. Finally, it was determined that, while the strength of the convection in the overlying liquid depends on the square root of its height, one need not model the entire domain to predict channel defects.
dc.language.isoen_USen_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.subjectEngineering, Mechanical.en_US
dc.subjectEngineering, Metallurgy.en_US
dc.subjectEngineering, Materials Science.en_US
dc.titleOn the length-scale and location of channel nucleation in directional solidificationen_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.grantorUniversity of Arizonaen_US
thesis.degree.leveldoctoralen_US
dc.identifier.proquest3050339en_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineMaterials Science and Engineeringen_US
thesis.degree.namePh.D.en_US
dc.identifier.bibrecord.b42728137en_US
refterms.dateFOA2018-06-26T11:24:50Z
html.description.abstractThis work provides evidence that channels in directionally solidified hypoeutectic Pb-Sn alloys nucleate at the dendrite tips. Using a finite-element simulator, distinctive 'convective signatures' are shown to exist for convectively unstable cases, where the instability of a system is shown to be largely a function of the thickness of an inverted density layer that exists ahead of the moving solidification front. With D the diffusion coefficient in the melt and V the solidification rate, the thickness of this layer, and therefore the stability of the systems studied, is shown to be a function of the length scale D/ V, where it is shown that channeling can be turned on or off simply by changing this length scale. This work also validates a finite element model of dendritic solidification by comparing predicted results to data resulting from eleven directionally solidified hypoeutectic Pb-Sn samples, which were produced under various thermal gradients and solidification rates. For all but one of the cases, which was thought to be borderline between channeling and not channeling, predictions of whether channel defects formed were supported by experiments. Finally, it was determined that, while the strength of the convection in the overlying liquid depends on the square root of its height, one need not model the entire domain to predict channel defects.


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