Unidirectional solidification of Al-Cu eutectic with the accelerated crucible rotation technique

The accelerated crucible rotation technique (ACRT) has been applied to the unidirectional solidification of AI-Cu eutectic to reveal the effect of for ced convection on the solidification microstructures by a systematic experi mental investigation combining different rotation methods (the maximum rota tion rate Omega(max) = 100-400 rpm) with various growth velocities(V-0 = 5- 60 mu m/s). The results can be concluded as follows: (1) Forced convection introduced by ACRT dramatically changes the eutectic microstructures. When the fluid flow is weaker (Re < 270), a great number of lamellar faults occu r in the eutectic; on the other hand, when the flow is stronger (Re > 500), fluctuation structure forms in the eutectic; (2) the lamellar spacing is n ot uniformly distributed in the radial direction of the solidified sample w ith ACRT, and the maximum spacing occurs near the crucible wall while the m inimum one at the center of the crucible. The average lamellar spacing obta ined by ACRT is smaller than that without ACRT and decreases upon increasin g the convection intensity (i.e. increasing Omega(max)); (3) whether or not a normal Bridgman process is performed before ACRT shows little influence on the growth of the nonfacet-nonfacet eutectic. (C) 1998 Elsevier Science B.V. All rights reserved.