Multimillion-Atom Molecular Dynamics Simulations of Superhard Nanocrystalline Ceramics

技术说明：材料研究部和数学科学部为该奖项提供资金，该奖项属于nsf范围内的数学科学优先领域。该奖项支持旨在阐明纳米晶陶瓷断裂和塑性的原子机制的计算和理论研究和教育。纳米碳化硅（n-SiC）具有高断裂韧性，金刚石- sic纳米复合材料（n-C-SiC）具有高硬度。晶界在纳米晶金属的变形过程中起着至关重要的作用。在n-C-SiC中，金刚石纳米颗粒与SiC基体之间的界面可能在决定力学性能方面起着关键作用。PI将在并行计算机上对n-SiC和n-C-SiC的纳米压痕和断裂进行百万原子MD模拟，以了解高硬度和韧性的原子机制。PI计划：表征响应机械载荷缺陷的成核和动力学。确定GB和体变形的作用。确定GB组织（如孪晶界）、GB扩散和滑动以及界面脱粘对硬度和断裂韧性的影响。PI还将计划开发和实施：创新的数据挖掘技术，如基于图的算法，以识别和跟踪由此产生的大量多元数据集中的拓扑缺陷。提出了一种基于温度加速MD、势能格局重构和反应路径采样的混合模拟方案，用于研究GB扩散等罕见事件。该研究计划将与培训和教育活动相结合。这些包括:1)为本科生和研究生提供涉及原子模拟和纳米实验的多学科培训；2)开设“纳米尺度材料高级模拟”课程，作为威斯康星大学工程物理系材料科学专业跨学科学位课程和计算科学与纳米工程新学位课程的一部分；(4)开展全校范围内的原子建模研讨会。非技术说明：材料研究部和数学科学部为该奖项提供资金，该奖项属于nsf范围内的数学科学优先领域。该奖项支持旨在了解陶瓷材料如何从组成原子开始断裂和变形的计算和理论研究。PI将专注于由许多纳米级颗粒组成的陶瓷材料。PI将使用涉及数百万原子的大规模计算机模拟技术，目的是了解特定材料的硬度如何取决于颗粒的大小，这些材料在施加机械应力时如何变形，以及最终如何创建既硬又耐断裂的材料。本研究对超硬材料的设计和纳米工程具有广泛的应用前景。拟议的研究还涉及开发先进的计算工具，包括能够长时间模拟和识别涉及材料变形的原子的特定排列的方法。该研究计划将与培训和教育活动相结合。这些包括研究生直接参与研究和开发跨学科的研究生和本科生水平的高级材料计算机建模课程。

TECHNICAL EXPLANATION:The Division of Materials Research and the Division of Mathematical Sciences contribute funding to this award which falls under the NSF-wide Mathematical Sciences Priority Area. This award supports computational and theoretical research and education seeking to elucidate the atomistic mechanisms of fracture and plasticity in nanocrystalline ceramics. Nanostructured silicon carbide (n-SiC) has high fracture toughness and diamond-SiC nanocomposites (n-C-SiC) have high hardness. Grain boundaries (GBs) play a crucial role in the deformation of nanocrystalline metals. The interfaces between the diamond nanoparticles and the SiC matrix in the n-C-SiC likely play a critical role in determining mechanical properties. The PI will perform multimillion-atom MD simulations of nanoindentation and fracture in n-SiC and n-C-SiC on parallel computers to understand atomistic mechanisms underlying high hardness and toughness. The PI plans to: Characterize the nucleation and kinetics of defects in response to mechanical loading. Determine the role of GB and bulk deformation. Identify the effect of GB structures (e.g., twin boundaries), GB diffusion and sliding, as well as of interfacial debonding on hardness and fracture toughness. The PI will also plans to develop and implement: Innovative data mining techniques, such as graph-based algorithms, to identify and track topological defects in the resulting massive multivariate datasets. A hybrid simulation scheme based on temperature accelerated MD, reconstruction of the potential energy landscape, and reaction path sampling to study rare events such as GB diffusion.The research program will be integrated with training and education activities. These include: 1) multidisciplinary training of undergraduate and graduate students involving both atomistic simulations and nano-experiments, 2) developing a course on "advanced simulations of materials at nanoscale", as part of the interdisciplinary degree of Materials Science Program and the new degree options in ComputationalScience and Nanoengineering in the Engineering Physics Department at the University of Wisconsin, (3) facilitating a cross-departmental curriculum in scientific modeling, and (4) developing campus-wide atomic-modeling seminar.NON-TECHNICAL EXPLANATION:The Division of Materials Research and the Division of Mathematical Sciences contribute funding to this award which falls under the NSF-wide Mathematical Sciences Priority Area. This award supports computational and theoretical research that seeks to understand how ceramic materials fracture and deform starting from the constituent atoms. The PI will focus on ceramic materials that are composed of many nanometer-sized grains. The PI will use large-scale computer simulation techniques involving millions of atoms with the aim of understanding how the hardness of specific materials depends on the size of the grains, how these materials deform when a mechanical stress is applied, and ultimately how to create a material that is both hard and highly resistant to fracture. The proposed research may have impact on the design and nanoengineering of superhard materials that have a broad range of applications. The proposed research also involves developing advanced computational tools including methods to enable simulation for long times and to identify specific arrangements of atoms involved in materials deformation. The research program will be integrated with training and education activities. These include the direct involvement of a graduate student in the research and developing interdisciplinary graduate and undergraduate level courses on advanced computer modeling of materials.