Solidification of undercooled Sn-Sb peritectic alloys: Part I. Microstructural evolution |
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Authors: | W P Allen J H Perepezko |
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Affiliation: | (1) United Technologies Research Center, 06108 East Hartford, CT;(2) Department of Materials Science and Engineering, University of Wisconsin-Madison, 53706 Madison, WI |
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Abstract: | The droplet emulsion technique, which involves dispersal of a bulk liquid alloy into a collection of fine droplets (5 to 30μm), was applied to Sn-Sb alloys to yield high levels of controlled undercooling. The maximum undercooling levels achieved
varied from 179 °C for pure Sn to 113 °C for a Sn-16 at. pct Sb alloy. Analysis of hypoperitectic alloy samples (alloys with
an Sb content less than that of the liquid at the peritectic temperature) indicates that solute trapping occurs during solidification
at the levels of undercooling and cooling rate investigated, yielding nearly homogeneousβ-tin solid solutions with compositions approaching those of the bulk alloys. With increasing undercooling and/or cooling rate,
hyperperitectic alloys exhibit a transition from a highly segregated structure consisting of faceted primary intermetallic
phase and cellularβ to a structure consisting primarily of a supersaturated tin-rich solid solution. Lattice constant measurements confirm that
virtually complete supersaturation ofβ-tin was achieved in emulsion samples cooled at 200 °C ss−1 for compositions up to approximately 20 at. pct Sb. The development and characteristics of subsequent solid-state precipitation
were used to guide the interpretation of the often complex solidification reaction sequences in the hyperperitectic alloys.
The formation of supersaturatedβ-tin solid solutions in the undercooled samples is related to the appropriate metastable phase equilibria and the development
of solute trapping.
Formerly Graduate Student, Department of Materials Science and Engineering, University of Wisconsin-Madison |
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