Atomistic and Mesoscale Modeling of Microstructure Development During Solid-state Sintering

Interfaces are ubiquitous in materials systems, and they influence the processing and properties of nearly all engineering and functional materials. Examples include grain boundaries (GBs) in polycrystalline materials, free surfaces in nanoparticles, and phase boundaries in multiphase materials. Therefore, understanding and controlling interfacial processes is a key aspect of materials design and discovery efforts. Recent developments in advanced manufacturing and synthesis techniques have enabled the fabrication of materials architectures with intricate nanoscale features. Of particular interest is solid-state sintering, known for creating complex and high-precision geometries with controlled microstructures. While sintering science has been the subject of active research, very little is known about the impact of GB geometry on sintering rates. Further, experimental studies on such manufactured nanostructured geometries demonstrated interfacial instabilities in which polycrystalline rod geometries break up, or pinch off, into isolated domains, a phenomenon reminiscent of the Plateau-Rayleigh instability in liquid jets. Through theoretical analysis, atomistic simulations, and mesoscale phase field (P–F) modeling, this work aims to unravel interfacial dynamics during sintering-based processing and under operating environments of nanostructured materials. First, we employ classical atomistic simulations to systematically examine the role of GB geometry in the sintering of Ni nanoparticles. Several metrics, such as particle neck width and principal curvatures, are used to quantify sintering rates as a function of GB character. Second, we develop a theoretical model to predict pinch-off instabilities observed in polycrystalline rod geometries. We complement such thermodynamic studies with P–F modeling, which provides insights into the kinetics of the pinch-off process. Predictions from our modeling results are compared with in-situ microscopy studies. It is shown that GBs play a destabilizing role in which the critical wavelength for the instability decreases with the increase in GB energy. Finally, we employ P–F modeling to investigate the role of local particle packing and associated GB network in microstructure formation and evolution during solid-state sintering. Morphological and topological metrics are used to quantify sintering rates and pore evolution. Simulation results reveal substantial variations in shrinkage rates as a function of particle packing. These studies suggest that local particle packing influences the resultant spatial distribution of porosity in sintered materials. In broad terms, the work in this thesis advances our understanding of interfacial dynamics in problems related to materials processing or stability under operating environments. This knowledge will enable the fabrication of advanced materials with controlled microstructures and tailored properties