Fracture and Stability of Metallic Nanotwinned Structures

技术概要：过去几年的研究提供了令人信服的证据，证明纳米孪晶金属与纳米晶和细晶粒金属相比具有非凡的性能。这些增强的特性中的一些包括超高屈服强度、高延展性、良好的导电性和高应变速率敏感性。这些特性使得纳米孪晶金属在结构应用中具有很高的吸引力。该项目的目的是通过集中的实验和计算建模工作，为纳米孪晶金属的稳定性和断裂机制提供定量的见解。这些关键问题，如果不解决，将限制这些纳米结构的金属和合金的实际应用，主要是由于对最佳性能的实现和稳定性的关注。为此，该项目的具体目标是研究孪晶界在纳米孪晶金属的脆性与韧性响应中的作用，并研究孪晶界介导的过程，如孪晶-孪晶相互作用和孪晶界处的裂纹/缺陷成核，以预测纳米孪晶金属最佳性能的临界孪晶层厚度。拟议的研究预计将对纳米结构金属科学和技术的几个重要领域产生影响，通过提供有价值的见解来了解控制其行为的变形机制。特别是，它将提供一个定量的理解到纳米晶和纳米孪晶金属的最佳结构性能，关于关键问题，如强度，延展性，稳定性和断裂机制。这种统一的实验、建模和制造工作的最终目标是开发用于批量合成纳米孪晶金属的工艺路线，这将实现它们作为下一代结构材料的潜力。拟议的研究还将有助于通过教育和外展工作丰富社区。从事该项目的研究生和本科生将在纳米力学和计算材料科学的多学科领域奠定坚实的基础。此外，通过这一项目取得的科学进展将被纳入研究人员在各自机构制定的课程。

TECHNICAL SUMMARY: Research over the past few years has provided compelling evidence for the extraordinary properties of nanotwinned metals as compared to their nanocrystalline and fine-grained counterparts. Some of these enhanced properties include ultra-high yield strength, high ductility, good electrical conductivity, and high strain rate sensitivity. Such characteristics make nanotwinned metals highly attractive materials for structural applications. The aim of this project is to provide quantitative insight into the stability and fracture mechanisms in nanotwinned metals by way of a focused experimental and computational modeling effort. These critical issues, if unaddressed, would limit the practical application of these nanostructured metals and alloys, largely due to concerns over the achievement and stability of optimal properties. To this end, the specific objectives of the project are to investigate the role of twin boundaries in the brittle versus ductile response of nanotwinned metals and to study twin boundary-mediated processes such as twin-twin interactions and crack/defect nucleation at twin boundaries, in order to predict the critical twin lamella thickness for optimal performance of nanotwinned metals.NON-TECHNICAL SUMMARY: The proposed research is expected to have an impact on several important areas of nanostructured metal science and technology by way of providing valuable insight into the deformation mechanisms governing their behavior. In particular, it will provide a quantitative understanding into the optimal structural performance of nanocrystalline and nanotwinned metals, with regards to critical issues such as strength, ductility, stability, and fracture mechanisms. The ultimate goal of this unified experimental, modeling and manufacturing effort is the development of processing routes for bulk synthesis of nanotwinned metals, which would realize their potential as next generation structural materials. The proposed research would also contribute to the enrichment of the community through education and outreach efforts. Graduate and undergraduate students working on the project, would develop a strong foundation in the multidisciplinary areas of nanomechanics and computational materials science. In addition, the scientific advances made through this project would be integrated into the coursework developed by the investigators at their institutions.