Cellular and dendritic growth: Part I. Experiment
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I,
INTRODUCTION
IN the past
10 to 15 years, there have been several studies aimed at developing theories of steady-state directional solidification of alloys. ~-s In such theories, both growth rate and temperature gradient are assumed to be controlled independently. Further, tip radius of curvature, tip temperature, and tip concentrations are predicted as functions of growth rate and temperature gradient. In previous works, however, attention has been given to primary or secondary arm spacing of dendrites, 6-~ and there are little published data of metallic systems available for comparison with theories. 6'9'~2'~3One of the most successful experiments was carried out by Burden and Hunt. '2 They measured the tip temperature of cells and dendrites under unidirectional solidification and developed a theory for dendritic growth. Their theoretical predictions of tip temperature were in good agreement with their own experiments. 2 In their theory, however, maximum growth rate criterion was assumed for the mechanism determining tip radius, whose physical meaning was not sufficiently elaborated. Trivedi3 and Kurz and Fisher proposed a new theoretical scheme in which interracial stability conditions on tip shape were explicitly considered. Both theories led to almost the same tip temperature dependence on growth rate, but predicted different order of magnitude for tip radius. In the present work, experimental studies have been carried out to obtain data on cellular and dendritic growth. Under constant temperature gradient, an aluminum-copper alloy was unidirectionally solidified. The tip radius of curvature, tip concentration, and primary arm spacing were also measured: The results are compared with current theories, and unique features with cells and dendrites are discussed.
YASUNORI MIYATA and TOSHIO SUZUKI, Associate Professors, with Faculty of Engineering, The Technological University of Nagaoka, 949-54, Nagaoka, Japan. JUN-ICHI UNO is with Chiyoda Chemical Engineering and ConstructiOn Company, Ltd., 108, Tokyo, Japan. Manuscript submitted June 25, 1984.
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METALLURGICALTRANSACTIONS A
II.
EXPERIMENTAL PROCEDURE
The alloy used in the present work was A1-4.1 mass pct Cu made with 99.99 pct aluminum and a A1-49.8 mass pct Cu master alloy. The alloy was cast into a small ingot (100 mm length and 30 mm diameter) and then drawn into thin rods of 5 mm in diameter. Specimens were prepared from these rods and their compositions were chemically analyzed. Each specimen was melted once and solidified in a graphite mold (300 ram, 5 mm inner diameter and 12 mm outer diameter) on a seed crystal with a (100) direction, so as to arrange the growth direction of dendrites in a uniform manner. Specimens were then unidirectionally solidified and water-quenched at a certain stage of solidification. The experimental set-up used was described in detail.~4 To measure temperature, two alumel-chromel thermocouples were fixed in the graphite mold. The temperature gradient, GL, and the growth rate, R, during solidification were determined
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