非共晶点合金跃迁加速定向凝固下耦合共晶组织生长的理论分析

THEORETICAL ANALYSIS OF AN ABRUPT INCREASE IN GROWTH RATE ON THE DIRECTIONALLY SOLIDIFIED MICROSTRUCTURES OF OFF-EUTECTIC ALLOYS

基于最高界面生长温度的判据,对定向凝固跃迁过程中非共晶点合金从共晶耦合区向非耦合区组织生长进行了理论分析,探讨了耦合共晶和初生枝晶之间的竞争生长.发现在共晶非共生区,跃迁加速定向凝固后的共晶组织仍可以耦合生长,给出了可能耦合生长的临界速率.另外,利用该理论对两种典型的共晶体系:Al-40%Cu层片共晶和Al-12%Ni棒状共晶合金进行了跃迁定向凝固耦合共晶组织生长分析,理论预测的临界速率与实验报道的结果基本一致.

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 A1-40%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.