Complex microstructures are ubiquitous in nature. The evolution of these microstructures alters their morphology and topology and thus very often dictates material properties, such as mechanical, electronic, thermal, and magnetic properties. Thus, in order to predict and control material properties, it is essential to have robust and efficient techniques to study microstructural evolution. Morphological characterization and phase-field simulation is utilized to study the evolution of complex three-dimensional two-phase mixtures, specifically dendritic and bicontinuous microstructures. A dendrite is a complex tree-like microstructure that commonly forms during solidification in metallic alloys. The secondary dendrite arm spacing (SDAS) has substantial influence on alloy hardness and tensile strength and the secondary arm tip-to-tip spacing (TS) can be used to quantify the degree of competitive side-branch behavior in dendritic evolution. Two-point statistics, which provide information about the spatial correlation of features in a dataset, are showcased as an efficient and unbiased way of extracting materials parameters from an Al-Cu alloy during solidification. Specifically, the evolution of dendrite primary arm thickness, average SDAS, and average TS are tracked using two-point Pearson auto-correlations of scaled mean curvatures. Nanoporous metals are prototypical bicontinuous microstructures that undergo coarsening when annealed at elevated temperatures. While coarsening of spherical particles has been extensively studied, relatively little is known about coarsening in more complex microstructures. A nanoporous gold sample that has a volume fraction at the limit of bicontinuity, where the structure begins to break up while still maintaining a high degree of connectivity, is examined. Coarsened nanoporous metals are commonly thought to have the same grain orientation of the original metallic sample. Phase-field simulation and morphological characterization is used to identify the process of particle detachment and reattachment as a mechanism for grain boundary formation as a nanoporous gold sample coarsens, demonstrating the development of an in-grain orientation spread and the critical role of the volume fraction of gold. Two-point statistics of bicontinuous structures are also used to study how the mass transport mechanism and volume fraction impacts the morphology of the two-phase mixtures.

Creator

• Elder, Kate Lauren Maud

DOI

• https://doi.org/10.21985/n2-wxr6-cg32

Subject

• Materials Science

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:15525
• etdadmin_upload_814831

Date created

• 2021-01-01

Resource type

• Dissertation

Rights statement

• In Copyright