Nanoscale solidification of metals by atomistic simulations: From nucleation to nanostructural evolution

Homogeneous nucleation during solidification in Al (fcc), Fe (bcc) and Mg (hcp) is studied by million-atom molecular dynamics (MD) utilizing the second nearest neighbor modified embedded atom method (2NN-MEAM) potentials. Spontaneous homogenous nucleation from the melt was produced without any influence of pressure, free surface effects and impurities. We also study the effect on the simulation size on homogenous nucleation and the heterogeneity in homogenous nucleation. The heterogeneity in homogenous nucleation originates from the twins, grain boundaries and short range order in the liquid during the initial stages of solidification. To study the solid-liquid coexistence in binary Al alloys, interatomic potentials for binary Al-Cu, Al-Fe, Al-Ni, Al-Mg, Al-Si and Al-Ge alloys were developed based on 2NN-MEAM formalism. Using these interatomic potentials, we compare formation energies, elastic constants, lattice parameters, enthalpy of solid and liquid mixing with experimental or first principle data of the binary Al alloys. In addition, we also compare the liquidus temperature of the Al-alloys from the phase diagram to the MD simulation. Finally, directional solidification of Al-11 at. % Cu is shown utilizing the 2NN-MEAM interatomic potential. The condition for directional solidification is produced by imposing dissimilar temperatures at the model boundaries along the [100] solidification direction to create a temperature gradient. Both the microstructural properties of solidified alloys and the mechanical properties under uniaxial tension is investigated”--Abstract, page iv