The Effect of Fluid Flow on the Eutectic Lamellar Spacing
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I.
INTRODUCTION
NUMEROUSworks ~-~7have been performed on the effect of fluid flow on the solidified micro- and macro-structure; these are mainly related to such topics as columnar-equiaxed transition 5'8'11-13 or the macro segregation 2-4'6'9'~~ caused mainly by the effects of flow on the dendritic growth morphology. However, little attention has been paid to the possibility of the modification of eutectic structure 1'17by the application of forced fluid flow during solidification. This is due to the fact that the dimension of the eutectic structure is usually on the order of several microns and it is, intuitively, hard to consider that the macroscopic flow would have any effect on the microstructure because of the formation of the "boundary layer", or the stagnant layer, at the solid-liquid interface, the size of which is several tens of times larger than the dimension of eutectic microstructures. However, recently it has been pointed out that the boundary layer should not be treated as a complete stagnant layer which is free from fluid flow. ~7Quenisset and Naslain I made a theoretical calculation predicting the change in lamellar spacing due to the application of forced convection during eutectic solidification. They reached the conclusion that the well-known relation between the lamellar spacing A and the solidification rate v, A2v = constant, should be modified when the strength of convection becomes large enough. The purpose of this work is to investigate experimentally whether the modification of the lamellar spacing is possible by the forced convection flow, and to examine the quantitative relation between A and v in such a case.
II.
EXPERIMENTAL
The experimental set-up is shown in Figure 1. About 700 grams of eutectic (Al-17 at. pct Cu) alloy using 99.99 mass pct aluminum and oxygen free copper were melted in an alumina crucible of 0.05 m ID and 0.16 m high. The depth of molten sample was about 0.1 m. The rotational fluid motion was generated by the application of rotating magnetic field by a two-pole three-phase coil. The power JIN JUNZE is Associate Professor, on leave from the Department of Metallic Materials and Technology, Dalian Institute of Technology, Dalian, China. K.F. KOBAYASHI, Associate Professor, and P.H. SHINGU, Professor, are with the Department of Metal Science and Technology, Kyoto University, Sakyo-ku, Kyoto, Japan. Manuscript submitted December 31, 1982. METALLURGICALTRANSACTIONS A
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( 1 )heater (2)2pole 3phase coil (3) ther rnocoupte (4)molten state alloy (5)alumina crucible (6),(7)water in (8),(9)water out (10 controllable motion device (11)seed crystal
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Fig. 1 --Schematic diagram of the experimental device.
supplied for the coil was up to 200 W, and the maximum rotation frequency of the molten sample was 10.5 rps. The unidirectional solidification was performed by lowering the crucible out from the furnace, applying, at the same time, the water cooling from the bottom. The rate of solidification was varied from 3.2 • 10 -6 m per second to 5 • 10 -5 m per se
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