Atomistic structure and lattice effects of vacancies in Ni-Al intermetallics

Atomistic computer simulation with embedded atom method potentials has been performed to study the energetics and structures of point defects in L1₂Ni₃A1 and B2 NiAl. The large size of Al atoms plays a dominant role in the relaxed atomic configurations of vacancies and antisite defects in the system. In both Ni₃Al and NiAl, it was found that excess Ni can be accommodated by Ni in Al sites. Accommodation of excess Al by locating Al in Ni sites is not energetically favorable in NiAl. The most stable di-vacancy configuration is two vacancies as first nearest neighbors in Ni sublattices for Ni₃Al and as second nearest neighbors in Al sublattices for NiAl. General attraction of two vacancies in Ni₃Al was found. On the contrary, vacancies in NiAl show repulsive interaction in several cases. This accounts for the existence of structural vacancies in B2 NiAl. The effects of different degrees of random disorder on the lattice parameters were evaluated, and it was found that these effects can be correlated with the local distortion around antisite defects using a simple model.