The behaviour of two different systems, NiZr2 and Cu3Au, submitted to a chemical disordering process under various thermodynamical conditions has been investigated by Molecular Dynamics simulations. The role played by volume expansion and elastic softening in the onset of the transition has been discussed in the framework of the percolation model (C.Massobrio and V.Pontikis, Phys.Rev.B 45 (1992) 2484), correlating the elastic instability with the percolation of the distorted regions which establishes in the lattice as a consequence of the external perturbations (introduction of defects, volume expansion, chemical disorder etc.).

By using isobaric-isothermal molecular dynamics and an n-body effective potential, we show that a dramatic elastic softening precedes the amorphization of NiZr2 occurring on chemically disordering the alloy. Above a critical level of chemical disorder, the shear elastic constant of the alloy increases suddenly up to a value comparable to the one of the amorphous solid obtained by quenching the liquid. This phenomenon occurs at the percolation threshold of the anelastically distorted regions surrounding the antisite defects. The percolation model describes satisfactorily experimental findings concerning the elastic softening and the loss of crystalline order in intermetallic compounds induced by irradiation or hydrogenation.

We propose a simple interatomic potential model for zirconium which successfully reproduces the phonon dispersion curves in both the α- and the β-phases as well as the temperature-induced phase transformation. Two interesting phenomena that help to understand the anomalous diffusion in the high-temperature β-phase are observed: the spontaneous formation of Frenkel-pairs and the highly correlated walk of the vacancy.

We calculate the shear elastic constants of the alloy NiZr2 by molecular dynamics simulations in the crystalline and amorphous phases as well as upon introduction of antisite defects in the crystal at T=300K. For S (long range order parameter) equal to 0.5, the system is amorphous and C' is larger than the same quantity relative to the crystal whereas C44 and C66 are smaller.