| Despite the fundamental and technological importance of microstructural evolution in polycrystalline multiphase materials, the majority of understanding has been achieved only in the isotropic limit, where boundary properties such as energy and mobility are isotropic. In contrast, it is well known that both energy and mobility of the boundaries can be strongly anisotropic, and the question is, how does this anisotropy influence the behavior of microstructural evolution of polycrystalline materials at elevated temperatures. Another question that will be briefly touched in this study is the presence of additional phases, such as voids, which introduces a number of additional diffusion paths (which, in general, can have very different diffusion rates) and results in the densification of the material. From the engineering point of view, the ability to control microstructural features of materials can lead to the design of potentially new materials with unique physical and mechanical properties.; Grain growth in systems of anisotropic grain boundary energy and mobility is investigated by means of both theoretical analysis and computer simulations. For the first time, energy and mobility are assumed to be both inclination- and misorientation-dependent. It is shown that mobility anisotropy alone does not change the growth kinetics in any significant way, nor the misorientation, size and edge distributions, even though grain shapes evolve in a non-self-similar fashion. It is the energy anisotropy that causes significant deviation of grain growth kinetics, misorientation and edge-distributions from the ones observed in isotropic systems. Size distributions are similar in all cases. Mobility anisotropy influences grain growth kinetics only when the energy is also anisotropic. Variation of the misorientation distribution with time plays the key role in determining the grain growth behavior.; Introduction of multiple diffusion paths and additional phases (vapor phase) is demonstrated on the example of sintering problem. More importantly, the model has been extended to take into account rigid-body motion of individual grains, which is a major reason for densification in porous polycrystalline systems. The new method is applied to the simple case of pore shrinkage to demonstrate its usefulness and compare with exact analytical solutions. |
