Modelling of prismatic grain growth in cemented carbides

A mean-field model dealing with prismatic grain growth during liquid phase sintering of cemented carbides with a Co-rich binder is presented. The evolution of the size of an assembly of non-spherical grains is obtained using a Kampmann-Wagner approach and by introducing a constant shape factor between the characteristic lengths of prisms. This factor is a function of interfacial energies of the two kind of facets, basal and prismatic, considered. The growth model is based on three different mechanisms, that can be rate limiting, taking place in series: 2D nucleation of a new atomic layer, mass transfer across the interface and long-range diffusion. The driving force for coarsening is distributed between the different facets. These equations are solved numerically, and the simulation results reveal that the specific abnormal grain growth phenomena experimentally observed in cemented carbides may be reproduced with this new more realistic description of the grain shape contrary to the spherical approach developed in the past. It is also shown that the initial powder size distribution, and more specifically its shape has a strong influence on the distribution of the driving force between the different rate limiting mechanisms and thus on the occurrence of abnormal grain growth. In that case, the self-similarity of the normalized grain size distribution over time is not achieved.