The effect of grain size on the nanocrystalline growth in metals and its simulation by Monte Carlo method

In this study, the thermodynamic stability of the grain boundaries and the grain growth of nanocrystalline Palladium (Pd) at 800 K were investigated. For this purpose, the Gibbs free energy curves of grain boundaries were plotted in terms of the excess volume by the use of Song’s, quasi-harmonic Debye approximation (QDA), and equation of state (EOS) thermodynamic models. The results of the two EOS and Song’s models showed that the excess volume increase up to values more than the critical excess volume, can result in the thermodynamic stability of nanocrystalline Pd. Therefore, according to the prediction of these two models, the nanocrystalline growth in metals was stopped at the grain sizes less than the critical grain size. But, according to the results of the QDA model there was no possibility for the stoppage of the grain growth and thermodynamic stability of the nanocrystalline Pd. To investigate the validity of the mentioned predictions, the Monte Carlo atomic simulation method was employed. The results obtained from the simulation confirmed the grain growth of nanocrystalline Pd within the size of the grains larger than the critical grain size and stoppage within the size of the grains less than the critical grain size.