KINETICS OF DEFECT RECOVERY AND LONG-RANGE ORDERING IN NI3AL-PROCESSES STUDIED BY ORDER-ORDER RELAXATION EXPERIMENTS(B .2. ATOMIC JUMP)

Fine isothermal relaxations of the degree of long-range order (LRO) in the homogeneous intermetallic compound Ni76Al24 + 0.19 at.% B (400 wt .ppm) were examined by means of residual resistometry. It was found th at two parallel relaxation processes are involved in the phenomenon. T he processes dramatically differed in the relaxation rates, but showed close activation energies exceeding 4 eV. A model explaining the occu rrence of two parallel relaxation processes and based on the vacancy t hermodynamics in L1(2) superstructure is proposed. The evaluated high activation energy for LRO kinetics is attributed to specific modes of vacancy diffusion involving jumps between different sublattices. It is compared with the activation energies of diffusion in Ni3Al exhibited by several ternary elements occupying the sublattice of Al. In these terms, the inadequacy of relating Ni diffusion data to the parameters of LRO kinetics in Ni3Al is indicated.