Monitoring micro-structural evolution during aluminum sintering and understanding the sintering mechanism of aluminum nanoparticles: A molecular dynamics study

In this work, molecular dynamics simulations have been performed to explore the structural evolution and underlying sintering mechanism of aluminum nanoparticles. The structural evolution during sintering was firstly monitored through radial distribution function and atomic migration, and the underlying sintering mechanism was further quantitatively characterized in terms of average displacement, mean squared distance (MSD), radius ratio (i.e., the ratio of the neck radius to the particle radius), shrinkage and radius of gyration, crystalline orientations, particle size, etc. Results show that the surface atoms of nanoparticles are more active than the internal atoms, favoring the mechanical rotation of nanoparticles during sintering. During the sintering process, average displacement, radius ratio and the shrinkage rate have undergone three stages with increasing the temperature: (1) a slow increase and subsequent abrupt hike after reaching the sintering temperature; (2) an almost plateau region over a wide span of temperature; (3) finally a sharp increase again after reaching the melting temperature. In contrast, MSD remains basically unchanged before melting, close to zero, followed by a sudden increase after melting temperature. Although the radius of gyration also experiences three stages, nonetheless it exhibits almost completely contrary trend. It has also been found that both sintering temperature and melting temperature demonstrate an almost linear increase with the increase of nanoparticle size ranging from 4.0, 6.0, 8.0 to 10.0 nm in diameter. Finally, we also found that the particle direction has limited effect on neck growth during sintering.