Dendritic growth of undercooled nickel-tin: Part I |
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Authors: | Y Wu T J Piccone Y Shiohara M C Flemings |
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Affiliation: | (1) Department of Materials Science and Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA;(2) Materials Processing Center, Massachusetts Institute of Technology, 02139 Cambridge, MA;(3) Castings Research Laboratory of Waseda University, Tokyo, Japan |
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Abstract: | Solidification of undercooled Ni-25 wt pct Sn alloy was observed by high-speed cinematography and results compared with optical
temperature measurements. Samples studied were rectangular in cross-section, and were encased in glass. Cinematographic measurements
were carried out on samples undercooled from 68 to 146 K. These undercoolings compare with a temperature range of 199 K from
the equilibrium liquidus to the extrapolated equilibrium solidus. At all undercoolings studied, the high-speed photography
revealed that solidification during the period of recalescence took place with a dendrite-like front moving across the sample
surface. Spacings of the apparent “dendrite” were on the order of millimeters. The growth front moved at measured velocities
ranging from 0.07 meters per second at 68 K undercooling to 0.74 meters per second at 146 K undercooling. These velocities
agree well with results of calculations according to the model for dendrite growth of Lipton, Kurz, and Trivedi. It is concluded
that the coarse structure observed comprises an array of very much finer, solute-controlled dendrites. |
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