KINETICS OF LONG-RANGE ORDER RELAXATION IN Ni_3Al: THE EFFECT OF STOICHIOMETRY

摘要

The isothermal relaxation of long-range order (LRO) after small temperature changes has been investigated in Ni_3Al intermetallic compounds (with 24.6, 25.0 and 26.5 at/100 Al) by measurements of the residual electrical resistivity. The equilibrium residual electrical resistivities were found to be consistent with theoretically calculated values of the LRO parameter. The approach to equilibrium could be satisfactorily represented by a sum of two exponentials; the relaxation rate is minimum at the stoichiometric composition. The activation enthalpies of the two processes are not significantly different (2.63-2.88 eV); they do not display an important composition dependence. A model is proposed for explaining the existence of the two isothermal relaxation processes.