Orientation effects in shocked nickel single crystals via molecular dynamics

Shock wave propagation and crystal deformation features were examined in nickel single crystals using nonequilibrium molecular-dynamics simulations for three crystallographic orientations: 〈100〉, 〈110〉, and 〈111〉. Two Morse-type pair potentials and one embedded-atom method (EAM) empirical potential were used to describe bond forces for single crystal nickel atoms. The two Morse-type pair potentials yield more accurate elastic moduli of nickel than does the EAM potential. The dissipation mechanism leading to shear stress relaxation was investigated at the piston/particle speed up=2.5(ε/m)1/2, where ε is an energy parameter and m is the atomic mass. For shock propagation along the 〈100〉 orientation, the plastic waves overtook almost all elastic precursors for all three potentials. However, for wave propagation along both 〈110〉 and 〈111〉 orientations, elastic precursors followed by steady plastic waves were observed. A clearly discernible leading solitary wave train followed by an extended elastically deformed region was observed in the 〈110〉 orientation. The EAM potential and the pair potentials showed some differences in shock wave propagation. In terms of crystal deformation, the EAM potential showed a greater degree of plasticity than the pair potentials. The two Morse-type pair potentials showed comparable results with respect to wave propagation features and crystal deformation. The details of the atomistic changes associated with shock-induced elastic-plastic deformation are presented for all three potentials.