Theoretical analysis of an abrupt increase in growth rate on the directionally solidified microstructures of off-eutectic alloys

Coupled growth eutectic microstructures at an abrupt increase in growth rate in directional solidification of off-eutectic alloys have been analyzed based on the maximum interface growth temperature criteria. The abrupt growth rate possibly required for the growth of coupled eutectics during the abrupt increase in growth rate is obtained by considering the competitive growth between the eutectic and primary dendrites. The theoretical predictions show that the eutectics can grow out of coupled zone, differing from the conventional eutectic solidification concept that indicates the entirely coupled eutectics only form within the coupled zone. In addition, the theoretical analysis are employed in two kinds of regular eutectics such as lamellar eutectic in the Al-40%Cu hypereutectic alloy and rod eutectic in the Al-12%Ni hypereutectic alloy; a good agreement between the theoretical calculation results and reported experimental data has been achieved.