Hexagonal metals, such as magnesium and titanium with hexagonal close packed structure, have the potential for increasing the efficiency of fuel consumption because of their superior strength-to-density ratio. In particular, magnesium with a density low enough to make it 35 percent lighter than aluminum and 78 percent lighter than steel is perhaps the most appealing of these lightweight materials. Replacing steel structural materials with magnesium-based materials in automotive applications would boost fuel efficiency by more than 50 percent. However, magnesium's use remains fairly limited because of a gap in the knowledge of a phenomenon called twin-twin interactions. Twins are specific features in hexagonal materials that can occur from the nanoscale to microscale and responsible for what is called deformation twinning, which is a major mode of plasticity in magnesium and responsible for its low strength and poor deformability. This research will focus on understanding the effect of twin-twin interactions on the mechanisms of deformation in magnesium by performing modeling at multiple scales supported by experimental observations. The outcome will be a predictive model that would allow engineers and scientists to optimize the processing routes of hexagonal metals for specific structural and environmental applications. As part of this research, students will be provided an opportunity to be trained at a national laboratory. Undergraduate students from underrepresented groups will be hired as part of the research team, and K-12 students will be exposed to the research through outreach events.
The long-term goal of this research is to establish a research framework for quantitatively characterizing and predicting the twinning induced microstructures and mechanical properties of hexagonal materials. It will link the macroscopic plastic responses to the crystallographic mechanisms causing them, while also accounting for microstructure evolution. To do so, the research team will characterize microstructures of twin-twin boundaries at the atomic level through atomistic simulations and transmission electron microscopes; identify twin-twin boundaries dominated deformation mechanisms at the atomic-/micro-scales by using atomistic simulations and in situ nanomechanical testing in scanning electron microscopies; establish twin-twin interaction models at the meso-scale by combining in situ mechanical testing and finite element analysis, and implement the meso-scale models into macro-scale effective-medium polycrystal plasticity models. The numerical and experimental tools developed through this project will eventually enable design of manufacturing processes for specific structural and environmental applications.
