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Primary arm spacing in directionally solidified Pb-10 wt pct Sn alloysThe dependence of primary arm spacings on growth speed was investigated for cellular and dendritic arrays in Pb-10 wt percent Sn samples directionally solidified under a constant positive thermal gradient in the melt. The gradient of constitutional supercooling was varied from almost zero (near the break-down of the planar liquid-solid interface at small growth speeds, cellular morphology) to near unity (large growth speeds, dendritic morphology). The spatial arrangements of cells and dendrites, as given by their coordination number, are not very different from each other. It appears that primary arm spacing maxima and the cell to dendrite transition are strongly influenced by the magnitude of the solute partition coefficient. The planar to cellular bifurction is supercritical in Pb-Sn which has a high partition coefficient, as compared to the subcritical behavior reported in Al-Cu and succinonitrile-acetone, both of which have low partition coefficients. The primary arm spacing model due to Hunt agrees with the experimentally observed trend for the whole growth regime. There is a good quantitative agreement at higher grdients of supercooling. However, the model overpredicts the primary arm spacings at low gradients of constitutional supercooling.
Document ID
19900036658
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Chopra, M. A.
(NASA Lewis Research Center; Cleveland State University OH, United States)
Tewari, S. N.
(Cleveland State University OH, United States)
Date Acquired
August 14, 2013
Publication Date
January 1, 1990
Subject Category
Materials Processing
Report/Patent Number
AIAA PAPER 90-0740
Accession Number
90A23713
Funding Number(s)
CONTRACT_GRANT: NCC3-95
Distribution Limits
Public
Copyright
Other

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