Exotic eutectic microstructures

Abstract

Solidification of eutectic systems delivers compelling examples of microstructure formation, which makes the phenomena intriguing to many engineers and scientists. Therefore, eutectic solidification is extensively studied experimentally, theoretically, and numerically. However, some exotic eutectic microstructures are still not understood, particularly the systems that exhibit anisotropy. The main objective of this thesis is to explore the microstructure formation in exotic systems during solidification. As directional solidification is a convenient way (imposes the temperature gradient, solidification velocity accurately and independently) to study the microstructure formation, the first part of the work was directed towards the development of directional solidification configuration. Subsequently, we investigated the microstructure formation in three different exotic eutectic systems. In the first system (Sn-Zn eutectic), we study the formation of two-phase microstructures with endeavors to bring new inferences, as the volume percentage of the (Zn)-phase in the eutectic is less than 10%, so one would expect it to form rods in the matrix of (Sn)-phase; instead, thin lamellae are observed. We claim that the rod-lamellar transition and well-defined lamellar orientation are due to the anisotropy of the free energy of the solid-solid interfaces. We deploy various methods/experiments for confirming the evidence of solid-solid interface anisotropy. We also provide the crystallographic orientation relationships between BCT-(Sn) and HCP-(Zn) in steady-state microstructures. In the second system (SnTe-Te eutectic), we investigate the evolution of complex patterns due to the addition of ternary impurities in the Sn-Te eutectic system that contains trigonal (Te) and an intermetallic SnTe phase with a cubic crystal structure. In this work, we examine the origin of such a microstructure that arises due to a two-phase growth instability induced by impurity addition. The binary eutectics (Sn-Te) and ternary eutectics (Sn-Te...