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Grain growth in two- and three-dimensional nanocrystalline materials is modeled by modifying the Monte Carlo Potts method based on the assumption that grain boundaries as well as triple junctions can be rate limiting during coarsening. To that aim each type of junction-associated lattice points (grain boundary-associated and triple junction-associated) is assigned an own specific mobility and energy. For the first time the influence of triple point (in 2D) and triple line (in 3D) energy and mobility on the grain growth kinetics is shown in detail. The results deviate clearly from normal grain growth kinetics but are in agreement with experimental studies as well as theoretical predictions. [ABSTRACT FROM AUTHOR]

A phenomenological approach to model the size effect observed during grain growth in nanocrystalline materials is presented. To that aim, the standard Monte Carlo Potts model is modified such that the mobility of grain boundaries depends on their triple junction distance. For initially very small grains growth kinetics are observed that are in agreement with experimental results, theoretical predictions and another simulation approach using a direct modification of the triple junction mobilities. [ABSTRACT FROM AUTHOR]

Abstract: The process of mechanically activated disproportionation by ball milling in hydrogen and subsequent desorption–recombination has been proved to be a promising method to produce nanocrystalline NdFeB-type magnets. To ensure a fully recombinated microstructure with homogeneous nano-sized Nd2Fe14B grains, the desorption–recombination processing temperature and time should be properly selected or optimized. Thus, Monte Carlo (MC) simulation was performed to elucidate the effect of processing temperature on the kinetics of the recombination reaction to form Nd2Fe14B phase as well as the growth of the recombinated Nd2Fe14B grains. Based on the recombination reaction and grain growth mechanism of the disproportionated NdFeB alloy, a modified Monte Carlo (MC) model was introduced to simulate the kinetics of the reaction and grain growth behavior under various desorption–recombination processing conditions. The results show that the kinetics of both the recombination reaction and the growth of the newly formed Nd2Fe14B grains accelerate with increasing temperature. In particular, the recombination reaction of the disproportionated stoichiometrical Nd2Fe14B (atomic ratio) alloy can be completed in 30min at 800°C, with the grain size of the recombinated Nd2Fe14B phase being 35nm in average. After the finish of the recombination reaction, the growth of the Nd2Fe14B grains will proceed, with the growth rate or kinetics depending on the processing temperature. This paper presents an effective way to simulate the reaction progress and the grain growth during the desorption–recombination processing of nano-structured as-disproportionated NdFeB alloy, which is useful for process control and optimization. [Copyright &y& Elsevier]