Diffusion by vacancy mechanism in Ni, Al, and Ni3Al: Calculation based on many-body potentials

The self-diffusion coefficients for the monovacancy mechanism, described in terms of the Arrhenius law, are calculated for Ni, Al, and the intermetallic compound Ni3Al by computer simulation techniques. Many-body interatomic potentials, based on the embedded atom model, are used together with the static relaxation method to study the static and dynamic properties of vacancies. The defect formation and migration energies, their corresponding relaxation volumes and vibration entropies, are evaluated. Special interest is devoted to the results obtained for Ni diffusion in Ni3Al. The present calculations predict that simple vacancy-Ni atom interchange jumps (both of ordered and disordered types) are energetically more favourable than the correlated six-jump cycles. Even though a difference in energies of delta = 0.35 eV favours migration via ordering jumps with respect to disordering jumps, the entropy factors behave in an opposite way suggesting that both types of jumps contribute to the Ni diffusion. Only for low temperatures (T less than or equal to 770 K) disordering jumps can be neglected. For this case: a pre-exponential factor D-0 = 0.2 x 10(-4) m(2) s(-1) is obtained.