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Nanocrystalline (NC) materials are intrinsically unstable against grain growth. Significant research efforts have been dedicated to suppressing the grain growth by solute segregation, including the pursuit of a special NC structure that minimizes the total free energy and completely eliminates the driving force for grain growth. This fully stabilized state has been predicted theoretically and by simulations but is yet to be confirmed experimentally. To better understand the nature of the full stabilization, we propose a simple two-dimensional model capturing the coupled processes of grain boundary (GB) migration and solute diffusion. Kinetic Monte Carlo simulations based on this model reproduce the fully stabilized polycrystalline state and link it to the condition of zero GB free energy. The simulations demonstrate the emergence of a fully stabilized state by the divergence of capillary wave amplitudes on planar GBs and by fragmentation of a large grain into a stable ensemble of smaller grains. The role of solute diffusion in the full stabilization is examined. Possible extensions of the model are discussed. 

We demonstrate using theoretical, computational, and experimental studies a morphological instability, in which a polycrystalline nanorod breaks up at grain boundaries (GBs) into an array of isolated domains. Our theoretical model is used to establish a neutral stability surface demarcating stable and unstable perturbations. It is shown that GBs play a destabilizing role in which the critical wavelength for the instability decreases with the increase in the GB energy. We carry out phase field simulations, which reveal accelerated pinch-off kinetics with the increase in the GB energy and predict temporal evolution of interfacial profiles in quantitative agreement with experimental observations.