Molecular-dynamics study of amorphization by introduction of chemical disorder in crystallineNiZr2

Abstract

By means of constant-temperature, constant-pressure molecular dynamics, we investigate the crystal-to-amorphous transformation of the intermetallic alloy ${\mathrm{NiZr}}_2$ resulting from the introduction of antisite defects. We constructed an n-body potential in the framework of the second-moment approximation of the tight-binding description of the electronic density of states. This modeling of the interatomic forces is successful in reproducing both static and thermodynamic properties of the real material. The imposition of chemical disorder quantified by the appropriate value of the long-range-order parameter, S, engenders a volume expansion followed by relaxation to a stationary state characterized by lower density and higher potential energy. The behavior of the pair distribution functions, g(r), reveals that amorphization takes place for values of S≤0.6, the corresponding volume expansion being of the order of 2%. Moreover the thermodynamic states obtained by chemical destabilization and rapid quenching from the liquid state are nearly identical. On the time scale of our simulations (${10}^{\mathrm{-}10}$ s), no detectable long-range diffusion of either species follows the introduction of chemical disorder. Some relevant features of the pair distribution functions (first and second peak positions, number of nearest neighbors) are in good agreement with those obtained experimentally from amorphous ${\mathrm{NiZr}}_2$ samples generated by rapid quenching.