On the mechanism of lamellar spacing adjustment in eutectic alloys

Abstract

Well controlled undirectional solidification experiments with continous increased rate were performed for eutectic alloys in the systems Ag-Cu, Al-Zn, Al-Cu and Al-Ni. In the Ag-Cu and Al-Zn alloys it was observed that discontinous changes in the lamellar spacing occured at low solidification rates. At high solidification rates such discontinuities could not be observed. Anyway the lamellar spacing always larger than observed at constant rate experiments. In Al-Cu alloys discontinous changes in the lamellar spacing with increasing solidification rate were also observed. However, after each change the lamellar spacing increased gradually up to a lamellar distance of 20% lower than before the abrupt decrease. All-Ni eutectic alloys gives a rod like eutectic structure. In this alloy no discontinous changes could be observed. A theoretical analyses of the observation based on well known theoretical models are discussed.