NSF/DMR-BSF: Twin boundary structure and mobility in shape memory alloys

该项目扩展了对材料如何变形的基本理解，并为开发新型和改进的合金提供了有价值的信息。这项工作中的活性或“智能”材料在医学（例如支架和牙套），车辆（包括汽车，飞机和航天器）和微机电系统（MEMS）中得到了应用。这是爱达荷州博伊西州立大学的一个美国团队和以色列海法理工学院的一个以色列团队之间的国际合作。该项目提高了对合金变形的基本理解，并培养了这一领域受过良好教育的劳动力。这促进了爱达荷州的经济发展，该州是美国人均国内生产总值（gdp）最低的州之一。此外，美国代表团将继续访问当地K-12学校的传统，并利用机构渠道招收代表性不足的少数民族学生，从而促进教育、科学和多样性。本科生和中等教育教师将通过博伊西州立大学本科生研究经验（REU）网站获得研究经验。该团队将通过同行评议的期刊、网站、会议和研讨会传播研究结果。该NSF-BSF合作研究项目包括爱达荷州博伊西州立大学的一个美国研究团队和海法以色列理工学院的一个以色列研究团队，扩展了对材料如何响应动态载荷的基本理解。除位错介导变形是塑性变形的主要方式之一外，对孪晶变形的研究尤为突出。虽然位错的动力学特性已经得到了很好的研究，但对孪晶界的相应知识并不存在，尽管这是现代材料的发展所需要的，包括高强度结构材料、纳米晶体材料、纳米尺度材料和功能材料，以配合材料基因组计划。国际团队的目标是将孪生边界（TBs）的动力学特性与其原子结构联系起来，其中包括拓扑缺陷，如孪生断开（TDs）。研究人员将利用新的实验和分析模型：(1)表征孪晶界结构；(2)建立I型和II型孪晶界缺陷模型；(3)测量孪晶界运动的完整动力学关系；(4)建立孪晶界运动的分析模型；(5)建立孪晶界结构特性与孪晶界动力学之间的关系。本研究计划旨在通过对TBs和TDs原子结构之间关系的全面理论和实验研究，促进材料科学和物理知识的发展；结核病和TD运动的障碍和机制；和TB运动的动力学关系。该团队将在三种不同的马氏体结构和三种不同类型的孪晶（化合物，I型和II型）中研究这些主题。研究结果将有助于建立I型和II型孪晶TBs复杂结构的精确模型，以及TBs的动力学关系。结果将是重要的，因为他们将适用于所有材料变形的孪生，包括金属间化合物，铁电陶瓷，形状记忆合金，和金属。美国和以色列的私人投资机构在相关学科上都有互补的研究项目，这些项目将从项目成果中受益。具体来说，美国PI正在进行孪生和疲劳研究，包括nsf资助的工作。以色列PI有一个关于铁材料孪生动力学的ISF项目，该项目与拟议的计划有一年的重叠。经验丰富的国际团队拥有开展拟议工作所需的知识和资源。

Non-technical AbstractThis project extends the fundamental understanding of how materials deform and provides valuable information for the development of novel and improved alloys. Active or "smart" materials such as those in this work find applications in medicine (e.g. stents and tooth braces), vehicles (including automobiles, aircrafts, and spacecraft), and in micro-electro-mechanical systems (MEMS). This is an international collaboration between a US team at Boise State University, Boise, Idaho, and an Israeli team at the Technion in Haifa, Israel. The project enhances the basic understanding of alloy deformation and develops an educated workforce in this area. This promotes the Idaho economy, with one of the lowest gross domestic product per capita in the US. Also, the US team will promote education, science, and diversity by continuing a tradition of visiting local K-12 school and using institutional channels for recruiting students from underrepresented minorities. Undergraduate students and secondary education teachers will gain research experience through a Boise State Research Experience for Undergraduates (REU) site. The team will disseminate results through peer-reviewed journals, websites, conferences, and seminars.Part 2: Technical description of the projectThis NSF-BSF collaborative research project which includes a US research team at Boise State University, Boise, Idaho, and an Israeli research team at the Technion, Haifa, extends the fundamental understanding of how materials respond to dynamical loading. In particular, research focuses on deformation by twinning, besides dislocation mediated deformation one of the major modes of plastic deformation. While the dynamical properties of dislocations have been well studied, a corresponding knowledge for twin boundaries does not exist though it is highly needed for the advancement of modern materials including high strength structural materials, nanocrystalline materials, nanoscale materials, and functional materials to align with the Materials Genome Initiative. The international team aims to correlate the dynamical properties of twin boundaries (TBs) to their atomistic structure, which includes topological defects such as twinning disconnections (TDs). Researchers will use novel experimental and analytical models to: (1) characterize twin boundary structures, (2) establish twin boundary defect models for type I and type II twins, (3) measure the complete kinetic relation of twin boundary motion, (4) develop analytical models for twin boundary motion, and (5) formulate relations between structural properties of twin boundaries and the dynamics of the twinning process. This research program proposes to advance knowledge in materials science and physics through a comprehensive theoretical and experimental study of the relationships between the atomistic structures of TBs and TDs; barriers and mechanisms for TB and TD motion; and kinetic relations for TB motion. The team will study these topics in three different martensite structures and three different types of twins (compound, type I and type II). Results are expected to facilitate accurate models of the complicated structures of TBs of type I and II twins, and the kinetic relations of the TBs. Results will be significant as they will apply to all materials that deform by twinning including intermetallic compounds, ferroelectric ceramics, shape memory alloys, and metals. Both US and Israeli PIs have complementary research projects on related subjects that will benefit from project results. Specifically, the American PI is conducting twinning and fatigue research including NSF-funded work. The Israeli PI has an ISF project on twinning dynamics in ferroic materials, which has one year of overlap with the proposed program. The experienced international team has the required know how and resources to carry out the proposed work.