Directional solidification and microstructures of near-eutectic Cr-Cr3Si alloys

Near-eutectic Cr-Cr3Si alloys were directionally solidified in a high-temperature optical floating zone furnace. At the eutectic composition, uniform and well-aligned lamellar structures were obtained over a fairly wide range of solidification conditions, but not at very low or very high growth rates where degenerate and cellular structures, respectively, were obtained. The lamellar spacing was found to increase with decreasing solidification rate, in agreement with the Jackson-Hunt theory. In addition, for a fixed growth rate, the lamellar spacing was found to increase with increasing rotation rate. The growth directions in the lamellar eutectic are found to be <1 0 0> for the Cr3Si phase and <1 1 1> for the Cr solid-solution phase. Eutectic microstructures (rod or lamellar) could also be produced at off-eutectic compositions, but only for a limited range of growth conditions. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.