  The resulting microstructure after the sintering process determines many
materials properties of interest. In order to understand the microstructural
evolution, simulations are often employed. One such simulation method is the
phase-field method, which has garnered much interest in recent decades.
However, the method lacks a complete model for sintering, as previous works
could show unphysical effects and the inability to reach representative volume
elements. Thus the present paper aims to close this gap by employing molecular
dynamics and determining rules of motion which can be translated to a
phase-field model. The key realization is that vacancy absorption induced
motion of grains travels through a grain structure without resistance. Hence
the total displacement field of a green body is simply the superposition of all
grains reacting in isolation to local vacancy absorption events. The resulting
phase-field model is shown to be representative starting from particle counts
between 97 and 262 and contains the qualitative correct dependence of sintering
rate on particle size.
