Adaptive Hierarchical Multiscale Framework for Modeling the Deformation of Ultra-Strong Nano-structured Materials

The topic of this project belongs to focus area #3 of the NSF solicitation: " Micro/Nanoscale Phenom-enology and Metrology. " Nano-structured materials are extremely attractive for applications requiring high strength and ductility. Two such areas are: (1) nano-layered composites for future aerospace applications demanding high strength-to-weight ratios; and (2) next-generation interconnect and packaging components in future electronic devices. While atomistic Molecular Dynamics (MD) simulations are the most reliable tools for investigating deformation phenomena at the nano-scale (in absence of electronic structure considerations, and with well-calibrated interatomic potentials), they are limited to very small volumes and short simulation times. Likewise, dislocation dynamics simulations are limited in the ability to resolve the core structure of defects and to incorporate dislocation nucleation events without ad hoc assumptions. We plan to develop an adaptive hierarchical multiscale framework (AHMF), where appropriate computational methods and physics models are selected adaptively based on error estimators. Using this framework, we plan to investigate the deformation characteristics of two classes of nano-structured materials: polycrystalline nano-twinned copper interconnects , and multi-layer nano-composites. We will apply these new tools to the design of bcc/fcc nano-layered materials, and the development of nano-twinned Cu interconnect lines with ultra-high strength and normal conductivity so that they can act as free standing interconnects. The models will be validated with ongoing experiments at UCLA, supported by a recent NSF-NIRT program. Intellectual Merit The mechanisms that control the dependence of the strength on the size of nano-crystals, or nano-laminates are not all understood, particularly for nano-laminates composed of duplex fcc / bcc crystal structure, and also for polycrystalline aggregates of sub-micron size copper crystals containing nano-twins. Nano-twinned Cu has ultra-high strength, but its conductivity is as good as coarse-grained Cu. Current computational methods are limited in their ability to simulate realistic nano-structured systems, because of severe requirements on the number of simulated atoms in MD, the required timescale for comparisons with experiments, and the ability to couple atomistic simulations to continuum methods. The intellectual content of the proposed research is summarized as: (1) discovery of the physical mechanisms that control strength and ductility at the nano-scale; (2) development of a rigorous adaptive hierarchical multiscale framework, with well-quantified error estimators; (3) contributing to the challenging concept of materials-by-design, which will ultimately change the way materials are optimized. Broader Impact The proposed project has direct applications to future nano-technology in two important sectors: future aerospace materials, and next generation …