Materials Science and Engineering PhD Thesis Defense bu Samira Mohagheghi

KOÇ UNIVERSITY

GRADUATE SCHOOL OF SCIENCES & ENGINEERING

MATERIALS SCIENCE AND ENGINEERING

PhD THESIS DEFENSE BY SAMIRA MOHAGHEGHI

Title: Dynamics of Eutectic Growth in a Three-Phase System

Speaker: Samira Mohagheghi

Time: January 30, 2018, 11:00

Place: ENG 208

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Res. Asst. Prof. Dr. Melis Şerefoğlu (Advisor, Koc University)

Prof. Dr. Mehmet Somer (Co-Advisor, Koc University)

Assoc. Prof. Dr. Murat Sözer (Koc University)

Assoc. Prof. Dr. Derya Dışpınar (Istanbul University)

Assoc. Prof. Dr. Sabine Bottin-Rousseau (INSP- Pierre and Marie Curie University (Paris VI))

Prof. Dr. Ersan Üstündağ (Istanbul Technical University)

Asst. Prof. Dr. Ehsan Layegh Khavidaki (MEF University)

Abstract:

Solidification microstructures, which are the traces left in the solid by the propagating solid/liquid interface, evolve depending on the inherent characteristics of the materials as well as the process parameters. The properties of materials are significantly affected by the microstructure therefore, understanding the pattern formation phenomena is necessary to control and optimize materials’ properties. The research effort explained in this thesis aims to understand the fundamental and crucial, but currently unknown, aspects of three-phase eutectic growth by performing systematic experiments on In-Bi-Sn ternary system. The employed methodology is based on real-time investigation of the three-phase eutectic growth dynamics using directional solidification techniques. In the first part of the thesis, the effect of sample thicknesses on the stability of the ABAC-type growth pattern, which is the basic state of the three-phase eutectic system in absence of interphase energy anisotropy, is investigated. The dynamics and features of the eutectic adjustment and the ABAC pattern recovery mechanisms are characterized. In the second part, the impacts of the interphase surface energy anisotropy on the microstructure selection are examined and characterized. Four types of three-phase eutectic grains are established as a function of interphase anisotropy.