Ultra-elastic and inelastic impact of Cu nanoparticles

a r t i c l e i n f o The degree of elasticity for the impact of a particle with a rigid wall is normally characterized with the restitution parameter, R. We examine such impact behavior of Cu nanoparticles with molecular dynamics simulations, for different particle sizes (1–15 nm in radius) and impact velocities (25–200 m s − 1). The impact can be ultra-elastic (R N 1) or inelastic (R b 1). Ultra-elastic or inelastic impact may occur for the smallest nanoparticles soly due to fluctuations, and the impact is inelastic but can be highly elastic (R ∼ 0.9– 1) for larger sizes. R decreases with increasing size and impact velocity in general. Impact-induced structure transitions (e.g., dislocations) can be reversible and induce irreversible heating regardless of their reversibility. Such heating along with remnant plasticity is the key mechanism for impact inelasticity. Inelastic impact may occur with little remnant plasticity. The impact of nanoparticles is of interest not only in impact physics [1,2] (e.g., the scaling laws for size and velocity), but also for such applications as coating, materials synthesis, nanotechnology and planet formation. Considerable experimental, theoretical and model-ing efforts have been dedicated to particle impact at different scales [2–10], and the literature can hardly be exhausted here. For instances, nanoparticle impact was modeled with molecular dynamics (MD) on the Lennard-Jones system [5,9], Si [6], ice [8] and Au [10], and experiments were conducted on ice particles [7], to investigate impact elasticity or inelasticity, coalescence and fragmentation. Nonetheless, MD simulations of nanoparticle impact still remain underexplored and are largely limited to extremely small nanopar-ticles and a few substances, and further studies are highly desirable for revealing novel impact phenomena and underlying physics. Impact of a particle with a rigid wall is normally characterized with the restitution parameter R [2]. R N 1, R = 1, and R b 1 represent ultra-elastic, perfectly elastic and inelastic impact, respectively. Here we utilize MD to simulate such impact behavior of a representative metallic system (Cu). We examine the impact elasticity of Cu nanoparticles and its dependence on particle size and impact velocity, as well as the related structure features. It is found that the impact of nanoparticles of Cu, one of the most ductile metals, can be ultra-elastic or exceptionally elastic. 2. Methodology We adopt an accurate embedded-atom-method potential [11] to simulate the impact of Cu nanoparticles on a rigid wall. …