Casting is a process in which liquid metal is poured into a mold and then allowed to cool and solidify. Cast alloys are used in many diverse applications, ranging from automotive parts to aerospace components. Porosity that arises during the solidification process has long been recognized as a critical factor in limiting the mechanical performance of cast alloys, especially under repetitive use that results in "fatigue" behavior. There is a strong drive towards minimizing porosity through a combination of casting design and optimization of the solidification process. To achieve that, a fundamental understanding of the underlying physics of porosity formation, growth and mobility and its impact on fatigue, and an enhanced predictive capability become necessary. This research addresses these needs through theoretical and computational modeling of processing and behavior at multiple length scales. Results from this research will lead to time- and cost-effective design and optimization processes that automotive, aerospace, and other industries can utilize to obtain better alloys and alloy components. This research features a synergistic approach based on materials science, manufacturing, and computational mechanics, which will expose graduate students to broader concepts and skills. Active focus will be given to ensure participation of underrepresented undergraduate students in research and outreach to high school students will strive to inspire interest in engineering education from an early age.
The objective of this research is to acquire a fundamental understanding of the mechanisms that govern porosity nucleation, growth, and migration during directional solidification process and employ that understanding to identify process-structure-property relations in cast alloys. This objective will be accomplished based on analysis and interpretation of existing solidification experimental data using theoretical and computational tools. Competing and contributing mechanisms that control porosity nucleation (solidification shrinkage and hydrogen segregation), growth (hydrogen diffusion, solidification front grow, and dendritic growth), and migration (buoyancy and thermocapillary effects) will be theorized and modeled. The multiscale computational framework, which will consist of a developed phase-field model and an existing internal state variable model combined with first-principles calculations, crystal plasticity, and the finite element method, will enable a phenomenological interpretation of the solidification process at multiple length scales. The accumulated constitutive descriptions will then be used to develop process-structure-property correlations.
