Dynamic mechanical contact behaviors and sintering mechanism of Al nanoparticles subjected to high-speed impact

In this work, dynamic mechanical contact behaviors and sintering mechanism of Al nanoparticles subjected to high-speed impact have been investigated using molecular dynamic simulations by analyzing radial distribution function (RDF), atomic average displacement, mean square displacement (MSD), the sintering neck radius, shrinkage, nanoparticle temperature and the proportion of amorphous atoms. The results shows that the long-ranged ordered structure of Al nanoparticles gradually transforms into short-range ordered structure and finally amorphous structure during the head-on impact. The atomic average displacement, MSD, radius ratio (x/R) and shrinkage at different initial impact speeds first experience a rapid increase to a maximum, followed by a slow decrease and subsequent a recovery to an almost constant. The displacement of surface atoms is always larger than the internal atoms during the head-on impact. There exists one critical impact velocity (e.g., 2800 m/s for given 4 nm in diameter) beyond which the ordered aluminum atoms completely transform into amorphous structure. The contact force, contact radius and contact stress obtained under a given low impact velocity and small strain are quite consistent with the predictions of the continuous Hertz model, but as the impact velocity and normal displacement further increase, the predictions of Hertz model underestimate these contact parameters. The influence of nanoparticle size on the relationship of contact radius and number of contacting atoms is inappreciable. The nanoparticles undergo elastic deformation, and then plastic deformation, followed by mechanical failure and shock-induced melting process into a whole. This work could strengthen our understanding of the industrial processes with applications in energetic nanomaterials, rocket propellant, metal sintering, etc.