Degree Type

Dissertation

Date of Award

2015

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

First Advisor

Ralph Napolitano

Abstract

While solidification structures with a large variety of morphologies and scales continue to be promising candidates for advanced applications in addition to the conventional ones, solidification science has been focused on understanding and building the bridges between theory and application, aiming to describe the solidification process at all length scales and enabling enhanced control over the final microstructure and resulting material properties. The knowledge of solidification built over the decades has been mostly based on simple cases like single phase formation one or two component or coupled growth in peritectic or eutectic alloys, whereas the understanding on much more complex multiphase solidification is very limited. As a result of this, multiphase structure formation, which has been mostly approached as extensions of the simpler cases mentioned above, has many open questions regarding dynamics of the process. Ternary alloys serve as a good example for the onset of understanding of multiphase solidification, where different kinds of reactions could take place along a solidification path. With additional degree of freedom, most of these reaction have different characteristic than their simpler counterparts, and many important aspects which can be disregarded for simpler cases come into play. The main goal of the present study is to understand and quantify the microstructural evolution during directional solidification of ternary Al-Cu-Ag system by focusing on different aspect of formation dynamics. Among many different possibilities with respect to phase and morphology, we focus ternary invariant eutectic, univariant coupled eutectic growth, and finally binary eutectic growth. The first challenge taken is quantification and parameterization of ternary invariant structures. Secondly, we focused on univariant two-phase coupled growth and examined the effect of convection, finally we study the texture selection in binary eutectic as an initiation of understanding this process in ternary and higher order eutectics. During our experimental studies, we have also come across two more subtopics which are important for comprehensive understanding of microstructural evolution. These are the quantification of the effect of solid state reaction causing deviation from the true solidifications in ternary invariant eutectic Al-Cu-Ag and the other one is effect of pre-holding period which alters the front and in results changing the initial stages of solidification which are carried until the end of the process.

Copyright Owner

Irmak Sargin

Language

en

File Format

application/pdf

File Size

189 pages

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