Solidification at the High and Low Rate Extreme

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The microstructures formed upon solidification are strongly influenced by the imposed growth rates on an alloy system. Depending on the characteristics of the solidification process, a wide range of growth rates is accessible. The prevailing solidification mechanisms, and thus the final microstructure of the alloy, are governed by these imposed growth rates. At the high rate extreme, for instance, one can have access to novel microstructures that are unattainable at low growth rates. While the low growth rates can be utilized for the study of the intrinsic growth behavior of a certain phase growing from the melt. Although the length ... continued below

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7310 Kilobytes pages

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Meco, Halim December 19, 2004.

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The microstructures formed upon solidification are strongly influenced by the imposed growth rates on an alloy system. Depending on the characteristics of the solidification process, a wide range of growth rates is accessible. The prevailing solidification mechanisms, and thus the final microstructure of the alloy, are governed by these imposed growth rates. At the high rate extreme, for instance, one can have access to novel microstructures that are unattainable at low growth rates. While the low growth rates can be utilized for the study of the intrinsic growth behavior of a certain phase growing from the melt. Although the length scales associated with certain processes, such as capillarity, and the diffusion of heat and solute, are different at low and high rate extremes, the phenomena that govern the selection of a certain microstructural length scale or a growth mode are the same. Consequently, one can analyze the solidification phenomena at both high and low rates by using the same governing principles. In this study, we examined the microstructural control at both low and high extremes. For the high rate extreme, the formation of crystalline products and factors that control the microstructure during rapid solidification by free-jet melt spinning are examined in Fe-Si-B system. Particular attention was given to the behavior of the melt pool at different quench-wheel speeds. Since the solidification process takes place within the melt-pool that forms on the rotating quench-wheel, we examined the influence of melt-pool dynamics on nucleation and growth of crystalline solidification products and glass formation. High-speed imaging of the melt-pool, analysis of ribbon microstructure, and measurement of ribbon geometry and surface character all indicate upper and lower limits for melt-spinning rates for which nucleation can be avoided, and fully amorphous ribbons can be achieved. Comparison of the relevant time scales reveals that surface-controlled melt-pool oscillation may be the dominant factor governing the onset of unsteady thermal conditions accompanied by varying amounts of crystalline nucleation observed near the lower limit. At high quench-wheel velocities, the influence of these oscillations is minimal due to very short melt-pool residence times. However, microstructural evidence suggests that the entrapment of gas pockets at the wheel-metal interface plays a critical role in establishing the upper rate limit. An observed transition in wheel-side surface character with increasing melt-spinning rate supports this conclusion.

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7310 Kilobytes pages

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OSTI as DE00835376

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  • Other Information: PBD: 19 Dec 2004

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  • Report No.: IS-T 2113
  • Grant Number: W-7405-Eng-82
  • Office of Scientific & Technical Information Report Number: 835376
  • Archival Resource Key: ark:/67531/metadc785419

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • December 19, 2004

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  • Dec. 3, 2015, 9:30 a.m.

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  • Jan. 9, 2018, 9:53 a.m.

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Meco, Halim. Solidification at the High and Low Rate Extreme, thesis or dissertation, December 19, 2004; Ames, Iowa. (digital.library.unt.edu/ark:/67531/metadc785419/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.