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Multiscale Modeling of Contact-Induced Plasticity in Nanocrystalline Metals

Challenges and Advances in Computational Chemistry and Physics, ISSN: 2542-4483, Vol: 9, Page: 151-172
2010
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Book Chapter Description

Predicting the integrity of metallic thin films deposited on semiconductors for microelectromechanical systems (MEMS) applications requires a precise understanding of surface effects on plasticity in materials with nano-sized grains. Experimentally, the use of nanoscale contact probes has been very successful to characterize the dependence of flow stress on mean grain size in nanocrystalline metals. From atomistic simulations, several models of plastic yielding for metal indentation have also been proposed based on the nucleation and propagation of lattice dislocations, and their interaction with grain boundaries beneath penetrating tips. However, model refinement is needed to include the characteristics of materials whose grain size is much smaller than the typical plastic zones found in contact experiments. Particularly, cooperative deformation processes mediated by grain boundaries, such as grain rotation, deformation twinning, and stress-driven grain coarsening, can simultaneously emerge for very small grain sizes (< 20 nm), thus making a predictive understanding of plastic yielding elusive. This chapter summarizes our recent progress in using multiscale modeling to gain fundamental insight into the underlying mechanisms of surface plasticity in nanocrystalline face-centered cubic metals deformed by nanoscale contact probes. Two numerical approaches to model contact-induced plasticity in nanocrystalline materials, the quasicontinuum method and parallel molecular dynamics simulation, are reviewed. Using these techniques, we discuss the role of a grain boundary network on the incipient plasticity of nanocrystalline Al films deformed by wedge-like cylindrical tips, as well as the processes of stress-driven grain growth in nanocrystalline films subjected to nanoindentation.

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