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Advisory Committee Chair

Amber L Genau

Advisory Committee Members

Charles Monroe

Robin Foley

John Griffin

Document Type

Thesis

Date of Award

2015

Degree Name by School

Master of Science in Materials Engineering (MSMtE) School of Engineering

Abstract

Even with decades of study, the complex development of solidification microstructures in cast iron is incompletely understood. Because Fe-C eutectic can produce different morphologies, and even different phases, depending on growth velocities and composition, understanding the conditions under which each forms are important. Directional solidification was used to observe the behavior of gray cast iron under carefully controlled solidification conditions. Specifically, alloys with industrially relevant amounts of silicon and manganese were studied, using a Bridgman furnace to investigate the effects of alloying additions and solidification velocity on graphite spacing and growth temperature of gray iron. An experimental technique for measuring the solid/liquid interface temperature was developed, producing precise temperature curves of the samples during the directional solidification. Average and minimum spacing for five compositions, containing varied amounts of Si and Mn, and velocities from 0.5 to 10 μm/s are reported. A critical velocity of around 1 μm/s was observed, above which the graphite structure loses directionality and austenite dendrites appear. A recently developed automated MATLAB algorithm was used for quickly and objectively measuring graphite spacing. The automated results compare favorably with traditional manual measurements and will allow for more robust measurement of eutectic spacing in a variety of systems where the spacing is highly irregular. Lastly, graphite spacing in gray iron was measured, showing a dependence on both velocity and composition. Adding silicon and manganese to the gray iron showed a decrease in spacing; while increasing the velocity seemed to affect directionality and reduce flake graphite thickness. Transverse section spacing and the carbon percentage versus distance of solidification analysis presented that graphite spacing and the carbon percentage varies with solidification distance.

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