COMPUTER-SIMULATIONS OF DISORDERING AND AMORPHIZATION KINETICS IN INTERMETALLIC COMPOUNDS

Molecular dynamics computer simulations on three intermetallic compoun ds, Cu,Au, Ni,AI and NiAl, have been performed to investigate the kine tics of the disordering and amorphization processes. These systems wer e chosen because reliable embedded atom potentials were developed for the constituent species and their alloys, and also because extended ex perimental results are available for them. Previous simulations of col lision cascades with 5 keV Cu and Ni primary knock-out atom (PKA) show ed a significant difference between the evolution of the short range o rder (SRO) and the crystalline order (GO) parameters in all of the int ermetallics: a complete loss of the crystalline structure and only par tial chemical disorder in the core of the cascade [T. Diaz de la Rubia et al., Phys. Rev. B 47 (1993) 11483; M. Spaczer et al., Phys. Rev. B 50 (1994) 13204]. The present paper deals with the simulation of the amorphization process in NiAl by 5 and 15 keV Ni PKAs. The kinetic ene rgy of the atoms in the simulated systems was removed on different tim e scales to mimic strong or weak coupling between electrons and phonon s. No evidence of amorphization was found at the end of the cascades c reated by the 5 keV recoils. However, the 15 keV PKA events showed tha t (i) in the no-coupling case the system evolved to a highly disordere d state, (ii) an amorphous region with about 100 non-lattice atoms was found in the case of weak coupling, (iii) the locally melted and recr ystallized region collapsed to a small dislocation loop when medium co upling was used and (iv) a highly ordered state resulted in the case o f strong coupling.