Computer simulation of lattice defects in Ni₃Al

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Virginia Polytechnic Institute and State University

Empirically estimated potentials were used to study the defects in Ni₃Al. A computer program which uses the conjugate gradient technique to obtain the relaxed structures was used. Atoms in the vicinity of the planar defects on the (111) plane were found to relax in two different oscillation modes namely the acoustic and optical modes. While the former is similar to the relaxation observed in pure Aluminum or Nickel, the latter was found to be a result of micromoments within the unit cell. The presence of atoms that differ in size and charge are believed to create micro-moments within each unit cell. The energy of a surface seem to depend directly on the atomic density of the terminating plane.

A vacancy prefers to be formed near the boundary rather than in the bulk. The formation of an Nickel vacancy is preferred, also a Nickel vacancy has more activation energy to migrate to the boundary. The effect of the Σ = 5 boundary seems to be felt only until a distance of approximately 5 Å away from the boundary.