THE STABILITY OF IRRADIATION-INDUCED DEFECTS IN NIAL

Vacancies, interstitials and antisite defects are produced in intermetallic compounds by irradiation with energetic particles. The manner in which these defects evolve during irradiation may contribute to microstructural changes such as the generation of dislocations, dislocation loops, voids, phase transformations and amorphization. In this work, the embedded-atom potentials for nickel and aluminum developed by Foiles, Baskes and Daw were used to calculate the energy of formation of antisite defects, of vacancies, and of various possible interstitial configurations in the B2 NiAl compound. The crowdion in the [111] direction that incorporates an extra nickel atom is found to be the lowest-energy interstitial configuration. Using the same potentials, the distance for spontaneous recombination of Frenkel pairs is found to be third-nearest neighbor provided the chemical order is maintained. However, if the chemical order of the sites nearest to the interstitial is altered at a bcc cell adjacent to the cell occupied by the vacancy at the cell center, recombination is inhibited in several cases in which the Frenkel pair is found to be stable. The implications of these results for irradiation-induced amorphization are discussed.