In situ observation of nonfaceted cellular growth in a narrow channel
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a temperature gradient, G. The temperature gradient was provided by a hot plate and a cold plate, kept at two constant temperatures and spaced at a certain separation. By this arrangement, the directional solidification condition is achieved. The setup, schematically shown in Figure 1, was placed on a transmission optical microscope stage, and the growth processes were observed directly. Details of the temperature gradient stage can be found elsewhere. [12.13] The material used was succinonitrile (NCCH2CHECN), which is a nonfaceting, transparent material, with a melting temperature of 58 ~ The as-received material was purified by zone refining prior to the experiment. A solution of succinonitrile-- 0.1 wt pct acetone was made by adding acetone ( C H a C O C H 3 , melting p o i n t - - 9 4 ~ to succinonitrile. The succinonitrile-acetone (SCN-ACE) alloy system was chosen because its main physicochemical properties have been reasonably accurately characterized. [14.~1 The material under investigation was contained in a PYREX* tube, about 167 /xm in inner
In Situ Observation of Nonfaceted Cellular Growth in a Narrow Channel
*PYREX is a trademark of Coming Glass Works, Coming, NY.
DONGKAI SHANGGUAN and JOHN D. HUNT Cellular growth is an important pattern formation process. It occurs when a planar solid/liquid interface breaks down due to instability of the planar interface, for example, as the growth velocity is increased or as the temperature gradient is decreased. Further away from the planar front stability condition, dendrites are formed. Nonfaceted cellular growth occurs in nonfaceting crystals, which include most metals and organic compounds, mostly with a relatively low entropy of fusion. Nonfaceted cellular array growth has been studied rather extensively. [1-8] Cellular/dendritic growth in metal-matrix composites, on the other hand, has only recently aroused interests, f9,1~ In particulate-reinforced metal-matrix composites, it has been suggested that the presence of particles may affect the microstructural evolution, tl~] In fiber-reinforced metal-matrix composites, e.g., A1-Cu/SiC, grains grow in the interstices between fibers, with a planar, cellular, or dendritic interface. It is anticipated that cellular/dendritic growth will be affected by the constrained environment in the interfiber region. In this communication, in situ observations were made of nonfaceted cellular growth in a capillary tube in an attempt to simulate cellular growth in the constrained environment in the interfiber region in metal-matrix composites. The capillary tube, containing a nonfaceting, transparent, organic compound, was sandwiched between a pair of glass slides. The same material was also contained in the glass cell outside the tube. A glass cell thus made was driven, at a constant velocity, V, through
DONGKAI SHANGGUAN, Assistant Research Engineer, is with the Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35487-0202. JOHN D. HUNT, Reader in Physical Metallurgy, is with the
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