Direct measurement of anisotropy of interfacial free energy from grain boundary groove morphology in transparent organic metal analog systems

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2005-01-01
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Rustwick, Bryce
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Materials Science and Engineering
Materials engineers create new materials and improve existing materials. Everything is limited by the materials that are used to produce it. Materials engineers understand the relationship between the properties of a material and its internal structure — from the macro level down to the atomic level. The better the materials, the better the end result — it’s as simple as that.
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Abstract

Both academia and industry alike have paid close attention to the mechanisms of microstructural selection during the solidification process. The forces that give rise to, and the principles which rule the natural selection of particular morphologies are important to understanding and controlling new microstructures. Interfacial properties play a very crucial role to the selection of such microstructure formation. Anisotropy of interfacial free energy (with respect to crystallographic orientation) is probably the most noticeable influence within the solidification of metallic systems. In the solidification of a metallic alloy, the solid-liquid interface is highly mobile and responds to very minute changes in the local conditions. At this interface, the driving force must be large enough to drive solute diffusion, maintain local curvature, and overcome the kinetic barrier to move the interface. Although it is generally accepted that the solid-liquid interfacial free energy and its associated anisotropy are highly important to the overall selection of morphology, the confident measurement of these particular quantities remains a challenge and reported values are scarce. The present study pertains to the measurement of the anisotropy of interfacial energy by comparison of experimental and theoretical GBG geometries in pure succinonitrile (SCN) and pivalic acid (PVA). A quantity of SCN and PVA was distilled, and zone refined using a process that is defined in the experimental procedure portion of this paper. Very thin slide assemblies were created and filled with these organic materials. For each system, several grooves were photographed and their shapes were compared with theoretical predictions. The correlation between experiment and theory was quantified and plotted as a function of the anisotropy for each of the GBG's examined, and a maximum correlation corresponded to the anisotropy of interfacial energy which describes that particular rotation of the GBG. The results from several rotations were statistically analyzed to ensure confidence in the measurement of the anisotropy of interfacial energy, and finally compared to reported values obtained with other techniques.

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Sat Jan 01 00:00:00 UTC 2005