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Theses and Dissertations - Department of Metallurgical and Materials Engineering

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Browsing Theses and Dissertations - Department of Metallurgical and Materials Engineering by Author "Brewer, Luke"

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    Prediction of heat transfer and microstructure in high-pressure die-cast A383 aluminum alloy
    (University of Alabama Libraries, 2019) Karkkainen, Mikko; Nastac, Laurentiu; University of Alabama Tuscaloosa
    Predicting the microstructure of the as-cast HPDC (high-pressure die cast) product is valuable, because micro-scale features often determine its mechanical properties. To predict the microstructure, the effect of processing parameters such as pressure and cooling rates must be known. The object of this study is to create state-of-the-art models for predicting heat transfer in the HPDC process, and apply those models to predict the evolution of one feature of the microstructure: the size of polyhedral α-Fe intermetallic phase. In the study, we develop a new empirical correlation for the Nusselt number in water cooling channels. This can be used to validate heat transfer coefficients for water cooling channels in commercial software to assist in modelling heat transfer in the HPDC process. Additionally, we develop a model for impact pressure in HPDC, which augments the state-of-the-art Hamasaiid model for peak IHTC (interfacial heat transfer coefficient) in HPDC, and relaxes some of their empirical assumptions. We integrate the IHTC model as a custom boundary condition in FLUENT 18.1 using SCM and UDF-files. Finally, we predict the size of polyhedral Fe-rich intermetallics using commercial casting simulation NOVAFLOW&SOLID for cooling rates and classical solidification theory for intermetallic size, and validate the results using optical micrograph size measurements.
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    Rapid Solidification of Austenitic Stainless Steels by Splat Quenching
    (University of Alabama Libraries, 2020) Morales, Sydney Mackenzie; Brewer, Luke; University of Alabama Tuscaloosa
    This thesis explores the phase transformations and microstructural evolution that are observed in rapid solidification of austenitic stainless steels by splat quenching. Splat quenching is an experimental method that produces rapidly solidified structures under cooling rates that are comparable to that of additive manufacturing. In additive manufacturing, specifically selective laser melting (SLM), metal is subjected to a very rapid heating and cooling that produces cooling rates in the range from 105-106 C/s. This rapid solidification produces microstructures that deviate from equilibrium. Five compositions of austenitic stainless steel with varying Cr/Nieq were studied to assess the effect of composition and cooling rate on the solidification microstructures that take place during splat quenching. The five compositions studied in this thesis were produced via arc melting to provide feedstock for splat quenching experiments. Splat quenched samples were analyzed for the presence of microsegregation, phase content, and solidification mode and morphology. Analysis techniques included electron dispersive spectroscopy, backscatter imaging, secondary imaging, and electron backscatter diffraction. Cooling rates achieved during splat quenching were evaluated utilizing electrolytic etching to estimate cell size of the solidification microstructures. Based on these analyses, the cooling rates were estimated to be in excess of 106 C/sec with a solidification velocity range of 0.1-1 m/s. The phase content of the splat quench microstructures as a function of alloy composition agreed well with the current rapid solidification literature.