Void drag model for Grain Growth
Multi-phase field (MPF) and molecular dynamics (MD) simulations have been applied to study nanograin growth mechanisms. At mesoscale level, prominent properties of nanostructured materials, e.g. the grain boundary excess volume and vacancy release, are inserted to MPF model using which we are able to investigate phenomenological aspects of the growth. The atomistic aspects of boundary movement and vacancy generation during the growth have been investigated using MD simulations.
MPF results confirm the linear grain growth in nano regime. MD simulations confirm these results. The Linear growth turns out that grain boundary mobility is independent from curvature. Considering vacancy diffusion as lower bound for the mobility, one can concludes that the linearity is a diffusion-limited phenomenon on the nano-sized structures. This is consistent with low-temperature linear grain growth.
The results explain linear grain growth in nanomaterials to be a diffusion-controlled process at low temperatures. At higher temperatures, however, linear regime switches to normal regime where curvature driven grain growth happens. The nature of excess volumes in grain boundaries plays the critical role in nanograin growth mechanisms.
A description of this research project in pdf format.
Mesoscopic grain growth simulations using the MPF model. 3D snapshots of the simulation box surface are shown.
redistribution of the excess free volumes as vacancies during the growth. The activation energy of the process is obtained to be less than one-tenth the self diffusion which is in correlation with experiments.