Resolving Twin-Slip Interaction Mechanisms in Hexagonal Close-Packed Metals

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Deformation of hexagonal close-packed metals, such as magnesium and titanium, involves complex activities of defects in the crystal structure, called twins and dislocations, respectively. Multiple modes of twinning and dislocation slip in crystal planes can be activated, even under simple mechanical loading. Interaction between twin boundaries and dislocations strongly influences the mechanical properties of these metals, but the physics behind the interaction is not understood. This award supports fundamental research on modeling the twin-slip interaction mechanisms, which are difficult to be resolved experimentally. The research will enhance fundamental understanding of the mechanical behavior of important engineering materials, such as magnesium and titanium alloys, that have shown promise in improving energy efficiency in automotive and aerospace applications. Insights obtained from the research will also help design new generation of lightweight alloys with improved strength and ductility. Additionally, the project will promote education and diversity by facilitating integrated computational materials engineering education for undergraduate and graduate students and by engaging underrepresented groups in STEM activities.Twin-slip interaction in metals with hexagonal close-packed crystal structures plays a crucial role in the mechanical properties of these materials. Such interaction has been considered an important factor in the hardening behavior during plastic deformation, but the mechanisms remain largely unknown. Twin-slip interaction occurs on the atomic scale. According to classical theory of deformation twinning, a one-to-one lattice correspondence exists between the parent and the product phase. Thus, if a dislocation in the matrix is transformed into a dislocation in the twin, the slip planes before and after twin-slip interaction must be corresponding planes. These corresponding planes can be unambiguously identified with atomistic simulations. The project will use atomic scale simulations to resolve lattice transformations during interaction between various twinning modes and dislocation modes in magnesium and titanium. By analyzing lattice correspondence, the interaction mechanisms can be resolved with clarity. Conditions for dislocation transmutation and dislocation absorption at different twin boundaries can also definitively be established. And the results obtained can be further extended to other important engineering metals such as zirconium and cobalt alloys.This project is jointly supported by the Civil, Mechanical and Manufacturing Innovations Division in the Engineering Directorate, and the Division of Materials Research in the Mathematical and Physical Sciences Directorate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.