ATOMISTIC SIMULATION OF POINT-DEFECTS AND DIFFUSION IN B2 NIAL .2. DIFFUSION MECHANISMS

In part I of this work we studied point defect energetics in the order ed B2 compound NiAl by means of computer simulations using 'molecular statics' and the embedded atom method. In the present paper we apply t he computation technique and results of part I to study atomic mechani sms of tracer self-diffusion in NiAl. We calculate the activation ener gy of Ni and Al self-diffusion in perfectly stoichiometric NiAl for th ree atomic mechanisms: the mechanism of next-nearest-neighbour (NNN) v acancy jumps, the 6-jump vacancy mechanism and the 4-ring mechanism. T he results of our simulations indicate that self-diffusion in stoichio metric NiAl is dominated by the mechanism of next-nearest-neighbour va cancy jumps. Diffusion of Al by this mechanism is likely to occur more slowly and with a higher activation energy than diffusion of Ni. The mechanism of 6-jump cycles is less favourable but still highly competi tive to the NNN vacancy mechanism. The 4-ring mechanism is the least e ffective for both Ni and Al diffusion. The effect of off-stoichiometry on diffusion in NiAl is briefly discussed.