Computer modeling of particle pushing and clustering during matrix crystallization

Two-dimensional cellular automaton computer simulations were carried out to model the geometric interaction between mobile, equiaxed particles and growing matrix grains, thus simulating crystallization (respectively, recrystallization, phase transformation or solidification) of a matrix material containing a mobile second phase (e.g. solid particles, liquid droplets or gas bubbles). The model allows the study of particle pushing by growing grains, which leads to particle accumulation and clustering at grain boundaries and triple points, and concomitant particle depletion within grains. Parameters explored are particle area fraction, particle settling speed, particle cluster mobility and grain nucleation rate under continuous nucleation conditions. These parameters are found to strongly affect the particle spatial distribution and clustering during and after crystallization. Conversely, the particles have no measurable effect on the grain shape or size. Finally, site-saturated nucleation at the boundaries of the simulation field is investigated, simulating e.g. solidification from crucible walls or recrystallization from sample edges. Pronounced clustering of particles takes place at grain boundaries and is further accentuated by particle settling.