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 Al-Cu eutectic to reveal the effect of forced convection on the solidification microstructures by a systematic experimental investigation combining different rotation methods (the maximum rotation rate Ω_max = 100-400 rpm) with various growth velocities (V₀ = 5-60 μm/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 occur 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 not uniformly distributed in the radial direction of the solidified sample with ACRT, and the maximum spacing occurs near the crucible wall while the minimum one at the center of the crucible. The average lamellar spacing obtained by ACRT is smaller than that without ACRT and decreases upon increasing the convection intensity (i.e. increasing Ω_max); (3) whether or not a normal Bridgman process is performed before ACRT shows little influence on the growth of the nonfacet-nonfacet eutectic.