Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Directional solidification studies have been carried out to characterize the spatial disorder in the arrays of cells and dendrites. Different factors that cause array disorder are investigated experimentally and analyzed numerically. In addition to the disorder resulting from the fundamental selection of a range of primary spacings under given experimental conditions, a significant variation in primary spacings is shown to occur in bulk samples due to convection effects, especially at low growth velocities. The effect of convection on array disorder is examined through directional solidification studies in two different alloy systems, Pb-Sn and Al-Cu. A detailed analysis of the spacing distribution is carried out, which shows that the disorder in the spacing distribution is greater in the Al-Cu system than in Pb-Sn system. Numerical models are developed which show that fluid motion can occur in both these systems due to the negative axial density gradient or due the radial temperature gradient which is always present in Bridgman growth. The modes of convection have been found to be significantly different in these systems, due to the solute being heavier than the solvent in the Al-Cu system and lighter than it in the Pb-Sn system. The results of the model have been shown to explain experimental observations of higher disorder and greater solute segregation in a weakly convective Al-Cu system than those in a highly convective Pb-Sn system.
Trivedi, R.; Mazumder, P.; and Tewari, Surendra N., "The Effect of Convection on Disorder in Primary Cellular and Dendritic Arrays" (2002). Chemical & Biomedical Engineering Faculty Publications. 14.
Trivedi, R., Mazumder, P., & Tewari, S.N. (2002). The Effect of Convection on Disorder in Primary Cellular and Dendritic Arrays. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 33, 3763-3775.
Copyright 2002 ASM International. This paper was published in Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 33, Issue 12, pp. 3763-3775 and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.
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This work was supported by NASA microgravity research, Division of Materials Science, Grant No. NASA NCC8-98.