KINETICS OF DEFECT RECOVERY AND LONG-RANGE ORDERING IN Ni_3Al + B--II. ATOMIC JUMP PROCESSES STUDIED BY 'ORDER-ORDER' RELAXATION EXPERIMENTS

摘要

Fine isothermal relaxations of the degree of long-range order (LRO) in the homogeneous intermetallic compound Ni_76Al_24+0.19at./100 B (400wt. ppm) were examined by means of residual resistometry. It was found that two parallel relaxation processes are involved in the phenomenon. The processes dramatically differed in the relaxation rates, but showed close activation energies exceeding 4 eV. A model explaining the occurrence of two parallel relaxation processes and based on the vacancy thermodynamics in Ll_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.