Grain-Size-Dependent Grain Boundary Deformation during Yielding in Nanocrystalline Materials Using Atomistic Simulations

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While the advantageous mechanical properties of nanocrystalline (NC) materials have stimulated numerous studies over the past decade, fewer studies have looked at the onset of yielding and deformation and the role of grain boundaries (GBs) prior to plastic flow. In this computational study, Ni microstructures with grain size between 6 nm and 20 nm were studied to elucidate the role of GBs during yielding. Residual strain was quantified by relaxing to zero stress during loading and calculating the resulting evolution of strain accommodation. The results of this work reveal the accumulation of plastic strain in GBs and how microplasticity changes with grain size, leading to the initiation of macroscopic yielding. Microplasticity accumulates homogeneously within large grain microstructures, then becomes localized with decreasing grain size. The resulting microstructural strain accommodation helps understand changes in the onset of dislocation plasticity and yielding behavior in NC materials and may have broader implications for their continual plastic deformation.