Term of Award

Fall 2025

Degree Name

Master of Science in Applied Engineering (M.S.A.E.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Manufacturing Engineering

Committee Chair

Jingjing Qing

Committee Member 1

Mingzhi Xu

Committee Member 2

Haijun Gong

Abstract

The benefits associated with the application of ductile irons are significantly attributed to the control of microstructures, with refinement of austenitic matrix during solidification playing a significant role. Nickel alloyed ductile irons are attractive due to their potential for high ductility and suitability for potential high-temperature applications with stable austenitic microstructure. Refinement of austenite grain structure is thus important to enhance the mechanical properties of the alloyed ductile iron. This research investigates the impact of in-mold additions of different alloying elements on the austenite morphology and grain refinement of nickel-alloyed ductile iron along with the associated mechanical properties. A hypoeutectic alloy with primary austenite phase was designed using thermodynamic calculations. Castings with different alloying additions were poured and were subject to different tests and analysis, assessing their solidification behavior, macrostructure, microstructure, and tensile properties. Macrostructure analysis of austenite revealed finer grain size with in-mold additions of Al, Ti, Ca, Bi, mischmetal, and Fe powder. Among these, Ti significantly increased the equiaxed grain proportions, making it the most effective and potent austenite refiner and the one that improved the mechanical properties the most. Inclusion analysis with scanning electron microscope equipped with energy dispersive x-ray and automated feature analysis revealed the impact of nitride inclusions to be more significant on the austenite refinement and strength enhancement in comparison to the other inclusions. On the contrary, Ca addition proved to be the least effective in terms of mechanical properties while both Al and Ca did not have significant impact to increase the size of the equiaxed zones even though some reduction in columnar grain size could be attained.

Research Data and Supplementary Material

No

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