: In situ observation of atomic scale twinning Process in HCP Crystals

: 原位观察 HCP 晶体原子级孪生过程

• 批准号: 1808046
• 负责人: Guofeng Wang
• 金额: $ 43.27万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1808046&HistoricalAwards=false
• 关键词: situ; observation; atomic; scale; twinning

NON-TECHNICAL SUMMARYPlastic deformation plays a crucial role in mechanical behaviors of crystals. Particularly, where the atoms are arranged in the pattern of hexagons, called hexagonal close packed metals and alloys such as magnesium or titanium-based alloys, twinning (two separate crystals having the same structure in a symmetrical manner) is an important type of plastic deformation, which critically influences the mechanical behaviors such as ductility, strength, work hardening, and fracture. As such, twinning has to be understood and controlled for designing and processing the hexagonal close packed metals and alloys. However, this has been impeded by the elusive understanding of atomic scaled mechanisms of twinning processes in the metals. Despite tremendous research efforts, for decades, how atom movements influence the mechanism of twinning remains poorly understood. The proposed research will employ high resolution transmission electron microscopy to investigate atomic-scale twinning processes in the materials, providing in-depth understanding on the role of atom movement in twinning of complex crystal structures. The project will provide important guidance for twinning-based alloy design and processing for achieving superior mechanical properties. Thereby, it will advance the application of light metal-based structures. The program will integrate research and education through training graduate/undergraduate students with diverse demographic backgrounds (particularly, female and minority) and their participation in national laboratories as well as outreach to elementary school through Pittsburgh Carnegie Science Museum.TECHNICAL SUMMARYTwinning plays a crucial role in mechanical behaviors of crystals. Particularly, in hexagonal close packed (HCP) metals and alloys, twinning, in addition to dislocation slip, can be profusely activated and critically influences their ductility, strength, work hardening, texture formation and fracture, primarily because twinning can carry deformation along the c axis of the HCP crystal where dislocation plasticity is limited. As such, twinning has to be controlled for designing and processing HCP alloys with improved mechanical properties. However, this has been impeded by the elusive understanding of atomic scaled mechanisms of twinning nucleation and growth in HCP crystals. In twinning, a part of the parent lattice is reoriented and the product lattice is mirrored by the parent about the twinning plane. Classically, such a lattice reorientation is achieved by a homogeneous simple shear which carries all or a fraction of the lattice points to the twin. The shear is mediated by coordinated movement of twinning dislocations on the twinning plane. The classical description of deformation twinning has been validated extensively in cubic structures. A significant difference in twinning of double-lattice structures, such as HCP, is that a twinning shear cannot carry all the parent lattice points to the twin positions. As a result, additional atomic movements, called shuffles, are required to accomplish twinning. Despite tremendous research efforts, for decades, how atom shuffles influence the mechanism of twinning remains poorly understood. Atomically-resolved direct experimental investigation are necessary for exploring the actual atomic shuffle and shear during twinning nucleation and growth, and hence obtaining a fundamental understanding on twinning mechanisms in HCP crystals. The proposed research will employ state-of-the-art in situ high resolution transmission electron microscopy (HRTEM) to investigate atomic-scale twinning processes in HCP crystals, such as twinning nucleation, growth and pertinent transformations as well as the orientation-dependent competition between dislocation plasticity and twinning at atomic resolution.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.

非技术总结变形在晶体的机械行为中起着至关重要的作用。尤其是，在原子以六角形的模式布置的地方，称为六角形的封闭封闭的金属和合金，例如镁或钛基合金，孪生（两个具有相同结构的独立晶体以对称的方式具有相同的结构）是一种重要的塑料变形类型，从而极大地影响了机械行为，例如，诸如义务，强度，实力，实力，实力，效果，效果。因此，必须了解和控制双胞胎，以设计和加工六角形的封闭式包装金属和合金。但是，这受到了对金属孪生过程原子缩放机制的难以理解的阻碍。尽管进行了巨大的研究工作，但数十年来，原子运动如何影响双胞胎的机制仍然知之甚少。拟议的研究将采用高分辨率的传输电子显微镜来研究材料中的原子尺度孪生过程，从而深入了解原子运动在复杂晶体结构孪生中的作用。该项目将为基于双重的合金设计和加工提供重要的指导，以实现出色的机械性能。因此，它将推动基于光金属的结构的应用。该计划将通过培训研究生/本科生的研究和教育，具有不同的人口统计背景（尤其是女性和少数群体）及其参与国家实验室，以及通过匹兹堡卡内基科学博物馆向小学推出。技术简要摘要在机械行为中起着至关重要的作用。尤其是，在六角形的封闭（HCP）金属和合金中，除了脱位滑移外，双胞胎还可以被大量激活，并严重影响其延展性，强度，工作硬化，质地形成和断裂，主要是因为双胞胎还可以沿着HCP晶体的C轴沿HCP晶体塑料量的HCP CAXIS携带。因此，必须控制双胞胎，以设计和加工具有改进的机械性能的HCP合金。然而，这受到了对HCP晶体中孪晶成核和生长原子缩放机制的难以理解的阻碍。在双胞胎中，将父晶格的一部分重新定位，并且父母在孪晶平面上反映了产品晶格。从经典上讲，这种晶格的重新定位是通过均匀的简单剪切而实现的，该剪切将晶格的全部或一小部分指向双胞胎。剪切是通过双胞胎平面上的双胞胎位错的协调运动来介导的。变形孪生的经典描述已在立方结构中得到了广泛的验证。双晶格结构（例如HCP）的孪生差异很大，是双剪剪物不能将所有父晶格点带到双位置。结果，需要其他称为洗牌的原子运动才能完成孪生。尽管进行了巨大的研究努力，但数十年来，原子的散热如何影响孪生的机制仍然知之甚少。原子分辨的直接实验研究对于探索在孪晶成核和生长过程中探索实际原子洗牌和剪切是必要的，因此需要对HCP晶体中的双胞胎机制获得基本的理解。拟议的研究将采用最先进的原位高分辨率传输电子显微镜（HRTEM）来研究HCP晶体中的原子级孪生过程，例如孪生成核，生长和相关变换，以及与脱位的异位和twine dection dection dectrution dection dections n sef Readers nesf之间的竞争相关的竞争。使用基金会的智力优点和更广泛的影响评估标准进行评估。

项目成果

Revealing shear-coupled migration mechanism of a mixed tilt-twist grain boundary at atomic scale

• DOI: 10.1016/j.actamat.2023.119237
• 发表时间: 2023-08
• 期刊: Acta Materialia
• 影响因子: 9.4
• 作者: Zheng Fang;Boyang Li;Susheng Tan;S. Mao;Guofeng Wang

Direct observation of dual-step twinning nucleation in hexagonal close-packed crystals

• DOI: 10.1038/s41467-020-16351-0
• 发表时间: 2020-05-18
• 期刊: NATURE COMMUNICATIONS
• 影响因子: 16.6
• 作者: He, Yang;Li, Bin;Mao, Scott X.
• 通讯作者: Mao, Scott X.