NSF-BSF: Stress-Assisted Structural Phase Transformations and Plasticity in Bicontinuous Nanomaterials

具有曲折表面和大表面积体积比的纳米多孔（NP）金属是各种重要先进技术的有希望的候选者，从电化学传感器/致动器和燃料电池过滤器到能量转换和存储系统。然而，NP金属的广泛技术应用的障碍是它们突然失效并且具有最小的均匀宏观塑性变形。该奖项支持基础研究，以探索通过替代相变（PT）机制实现双连续NP材料均匀变形的新方法。均匀的PT机制将防止局部变形，从而提高整个系统的延性。在这个项目中获得的见解将使强大的和韧性的NP材料的设计，利用亚稳相，不能在传统的大块金属和合金。该项目中阐明的基本机制将适用于其他耐火材料，也可以扩大规模，用于大规模的结构和功能应用。该奖项还将支持本科生暑期实习，为高中生探索纳米技术的研讨会，重点关注代表性不足的少数民族参与，以及国际学生交流。该项目旨在实现统一（而不是本地）PT的机制，并实现显著改善钼（Mo）基NP金属的塑性变形能力。需要极端的应力（在数十吉帕斯卡的量级上）来将Mo中的PT从低能量体心立方相（body-centered cubic phase）电驱动到高能量面心立方态，而不是激活位错成核或传播机制。虽然已经在局部和原子尺度上观察到这种PT，但仍然完全不清楚它是否可以均匀地发生，以显着改变尺寸大于约100纳米的试样的机械行为。该项目将研究微观结构特征的组合，包括1）小（无缺陷）韧带，2）结构的弯曲度，以及3）Mo和次要材料之间的界面，这将使高内应力在整个NP复合材料结构中均匀分布，并促进均匀变形和更好的延展性。分子动力学模拟和纳米力学测试实验与有限元分析将被整合，以研究潜在的PT为基础的均匀塑性变形的机械响应和死后微观结构。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Nanoporous (NP) metals with tortuous surfaces and large surface-to-volume ratio are promising candidates for various important advanced technologies, from electrochemical sensors/actuators and fuel cell filters to energy conversion and storage systems. However, a hindrance to widespread technological application of NP metals is that they fail suddenly and with minimal uniform macroscopic plastic deformation. This award supports fundamental research to explore new ways of enabling homogeneous deformation in bicontinuous NP materials via alternative phase transformation (PT) mechanisms. The homogenous PT mechanisms would prevent localized deformation and, thus, enhance ductility across the whole system. The insights to be gained in this project will enable design of strong and ductile NP materials by utilizing metastable phases which cannot be obtained in conventional bulk metals and alloys. The fundamental mechanisms elucidated in this project will be applicable to other refractory materials and can also be scaled up for large-scale structural and functional applications. The award will also support undergraduate summer internships, a workshop on exploring nanotechnology for high school students with focus on underrepresented minority participation, and international student exchange.This project seeks to enable mechanisms of uniform (instead of local) PT and achieve significantly improved plastic deformability in Molybdenum (Mo)-based NP metals. Extreme stresses (on the order of tens of gigapascals) are required to thermodynamically drive a PT in Mo from a low-energy body centered cubic phase to a high-energy face centered cubic state instead of activating dislocation nucleation or propagation mechanisms. While this PT has been observed locally and at the atomic scale, it remains totally unclear whether it can occur homogenously to significantly modify mechanical behavior of specimens larger than about hundred nanometers in size. This project will study the combination of microstructure features including 1) small (defect-free) ligaments, 2) tortuosity of the structure, and 3) interfaces between Mo and a secondary material, that will enable a uniform distribution of high internal stresses through the entirety of NP composite structures and promote uniform deformation and better ductility. Molecular dynamics simulations and nanomechanical testing experiments with finite elements analysis will be integrated to study the mechanical response and post mortem microstructures for potential PT-based uniform plastic deformation.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.