Computer Simulation of Grain Growth with Mobile Particles

[From the Introduction]

The microstructures of metallic and ceramic materials are known to be strongly influenced by the presence of second phase particles. Second phase particles may pin grain boundaries and hence may be used to limit grain size (l-4). When particles are mobile, grain boundary/particle interactions typically lead to an even higher density of grain boundary/particle intersections than with static particles. The present paper addresses the influence of mobile particles on grain size evolution in polycrystalline materials.

Particle mobility varies sensitively with particle size r (as l/r3 or l/r4) and temperature (in an Arrhenius manner) (5,6). Thus the effects of non-zero particle mobility on gram structure should be most easily observed at elevated temperatures and for small particles. Interactions between moving gram boundaries and mobile impurities has received considerable attention (e.g., (7-9)). These studies have shown that when the driving force on the gram boundary is small (or the impurity mobility is large), impurities diffuse to the moving boundary, and the boundary impurities move together, in a highly correlated manner. In this case, the boundary velocity will be small. But if the driving force on the boundary is large, or the impurity mobility is low, the boundary can escape the impurities and move at a much higher velocity In some cases, these two regimes are not easily distinguished.

In the present study, we employ a Monte Carlo simulation procedure to study grain growth in the presence of diffusing particles. This simulation procedure has been used to study a wide variety of grain growth phenomena (2-4,10-13). We examine the temporal evolution of the grain size and microstructure, and the influence of particle fraction, and temperature. The results are analyzed in terms of the relationship between the boundary driving force and the steady state boundary velocity.