Kinetics of strain relaxation in metallic glasses

Torque relaxation and strain recovery measurements under linear heating for three Fe-, Ni- and Co-based metallic glasses are presented. Torque relaxation is determined by the pre-annealing temperature, T_a: at T < T_a, the degree of relaxation is small and high-rate torque relaxation starts near T_a. Analogously, high-rate strain recovery starts near the temperature of preliminary homogeneous deformation. The temperatures where high-rate stress relaxation and strain recovery begins are calculated in the framework of an activation energy spectrum model and are consistent with experiment. A homogeneous-flow model is developed which qualitatively explains macroscopically reversible behaviour as a result of directed irreversible microscopic relaxation events with distributed activation energies.