Factors Affecting Stable Planar Growth During the Directional Solidification of Hypermonotectic Aluminum-indium Alloys. Ph.D. Thesis
Immiscible (monotectic) alloy systems have become materials of interest due to their unique potential applications, which include bearing materials, catalysts, permanent magnets, and fine particle superconductors. For some of these applications, a microstructure containing continuous aligned fibers is desired. In-situ fibrous growth has been observed in directionally solidified alloys of monotectic composition. However, for the proposed applications, a greater volume fraction of the fibrous phase is needed than is available in alloys of monotectic composition. In order to obtain this greater volume fraction of the fibrous phase, alloys of hypermonotectic composition are necessary. However, when alloys of hypermonotectic composition are directionally solidified, there are two factors which can disrupt in-situ fibrous growth. These factors are buoyancy-driven convection and constitutional supercooling. A theoretical model containing the effects of both convection and constitutional supercooling has been developed and applied to the immiscible aluminum-indium system. The resulting stability limit diagram predicts the theoretical composition limits for stable growth as a function of solidification front velocity. This research has concentrated on experimentally verifying the theoretical limits of stable growth. By directionally solidifying samples over a range of compositions and growth rates, the region of stable growth was determined by examining both the microstructure and the composition profile developed in the samples. The results indicate that the theoretical limits of stable growth predicted by the stability limit diagram are a conservative estimate of the region of stable growth.
- Research Organization:
- Alabama Univ., Birmingham, AL (United States)
- OSTI ID:
- 236784
- Report Number(s):
- N-96-21554; NIPS-96-34949; TRN: 9621554
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
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