Parallel molecular dynamics simulations of dynamics of oxidation and reactive wetting in metal/ceramic systems

Oxidation of a flat aluminum (111) surface and the reactive wetting of the aluminum (Al) droplet on a flat alumina (alpha-Al2O 3) surface are investigated by using parallel molecular-dynamics simulations with dynamic charge transfer among atoms on a microscopic length scale. The interatomic potential, based on the formalism of Streitz and Mintmire, allows atoms to vary their charges dynamically between anions and cations, when atoms move and their local environment is altered.We investigate the oxidation thickness as a function of time and the oxygen density which is 10--40 times that of the normal state (1 atm and 300 K). Stable amorphous oxide scales form around 51 A at 4.42 ns, 2.862 ns, and 2.524 ns, respectively, and molecular oxygen density 10--40 times the normal state. We also study structural correlations in the resulting final oxide scale. The structure of final oxide scales depend on depth, where density of aluminum (Al) and oxygen (0) atoms change.Reactive wetting of aluminum nanodroplet on alumina surface is also studied using parallel MD. We study heat transfer, diffusion within droplet, and the structure of the inter-metallic phases in the liquid-solid interface. Oxygen (0) atoms diffuse into the spherical aluminum (Al) droplet and form an interface between the flat solid substrate and the Al droplet. This diffusion of oxygen atoms may be the main source of adhesion between the Al drop and the flat alpha-Al 2O3 substrate. The temperature in the flat alpha-Al 2O3 bulk substrate rises from OK to 200 K at the end of the simulation, 8.5 ps, but the temperature becomes much higher at the reactive interface. We have examined which oxygen atoms from the substrate participate in the wetting and the formation of a solder joint at the Al/alpha-Al 2O3 interface.