Primary spacing selection and phase transformation in directional solidified Cu-21%Ce alloy

Abstract

In this study, a hyper-peritectic Cu-21 wt% Ce alloy was prepared by directional solidification method at various withdrawal rates of 100 μm s−1, 25 μm s−1, 6 μm s−1, 5 μm s−1, 4 μm s−1 and 2 μm s−1. The microstructure evolution was investigated by optical microscope. The phase constitutions were analysed by the x-ray diffraction, differential scanning calorimetry and transmission electron microscope. Further, the minimum spanning tree method was selected to investigate the spacing characters of dendritic arrays. The experimental results demonstrate that primary phase microstructure transforms from dendritic to island structure with decreasing the withdrawal rates, and the maximum volume fraction of the primary phase reached 45.16% at the withdrawal rate of 6 μm s−1. It was found that when reducing the withdrawal rate from 100 μm s−1 to 2 μm s−1, the primary dendrite spacing increased first and then decreased, with a maximum value of 144.64 μm presenting at 6 μm s−1. The phase constitutions in the directional solidified samples were confirmed to be Cu6Ce, Cu4Ce and Cu4Ce + Cu2Ce eutectics. Moreover, the maximum compressive force was determined to be 10.3 kN and the maximum compressive strain was 3.73% respectively, corresponding to the maximum primary phase volume fraction at a withdrawal rate of 6 μm s−1. Directional solidification method has been proved to be an efficient way to improve the mechanical properties of hyper-peritectic Cu-21%Ce alloy.