Sintering of particles: grain-growth and non-sphericity treated with DEM
Résumé
Sintering of ceramic powders is a high-temperature process that aims to densify an initially particulate material. The driving force is the reduction of the interfacial energy of the system. The same driving force leads to grain growth, which is generally considered detrimental. Here we explore the coupling between densification and grain growth at the particle scale. Simultaneously occurring shrinkage, surface diffusion, grain migration and particle coalescence are implemented in a DEM framework. The adopted model treats the main fluxes of matter through physics-based interaction laws. Small particles are gradually eaten away by larger ones, leading to coalescence and grain growth. The results of these simulations are compared to experimental data with good accordance of key features of microstructure evolution (densification kinetics, grain size-density trajectory, average grain size evolution). By taking advantage of the possibility to simulate initially a large number of particles (which gradually disappear with coalescence), the model elucidates the influence of the initial particle size distribution on the grain growth kinetics. Because ceramic particles are seldom spherical, we also implemented non-spherical particles using the Level-Set method. This is particularly important for sintering, as it is a curvature driven process. Contact detection, which is the critical step, is treated as an optimization problem, to reduce computational costs. The proposed implementation of LS-DEM is a proof of concept of its potential effectiveness for sintering. For illustration, simulations of packings of ellipsoidal particles with elastic and sintering interactions are described. The sintering simulations are used to analyze the influence of the particle aspect ratio, in particular on the shrinkage rate.
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