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

镁和钛等六方密排金属的变形涉及晶体结构中复杂的缺陷活动，分别称为孪晶和位错。即使在简单的机械载荷下，也可以激活晶面上的多种孪晶和位错滑移模式。孪晶界和位错之间的相互作用强烈地影响着这些金属的机械性能，但这种相互作用背后的物理原理尚不清楚。该奖项支持对孪生滑移相互作用机制进行建模的基础研究，这些机制很难通过实验解决。这项研究将加强对镁和钛合金等重要工程材料力学行为的基本了解，这些材料在汽车和航空航天应用中显示出提高能效的前景。从研究中获得的见解也将有助于设计具有更高强度和延展性的新一代轻质合金。此外，该项目将促进教育和多样性，促进本科生和研究生的综合计算材料工程教育，并让代表不足的群体参与STEM活动。具有六方紧密堆积晶体结构的金属中的双滑移相互作用对这些材料的机械性能起着至关重要的作用。这种相互作用被认为是塑性变形过程中硬化行为的一个重要因素，但其机制在很大程度上仍不清楚。孪生滑移相互作用发生在原子尺度上。根据形变孪生的经典理论，母相和产物相之间存在一一的晶格对应关系。因此，如果基质中的位错转变为孪晶中的位错，则孪晶滑移相互作用前后的滑移面必须是对应的平面。这些对应的平面可以通过原子模拟明确地识别出来。该项目将使用原子尺度模拟来解决镁和钛中各种孪生模式和位错模式之间相互作用时的晶格转变。通过分析晶格对应关系，可以清晰地解析相互作用机制。在不同的孪晶界面位错变形和位错吸收的条件也可以确定。该项目由工程局的土木工程、机械和制造创新司和数学和自然科学局的材料研究部联合支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.