Isothermal stress relaxation of bulk and ribbon Zr-based metallic glass

The results of density and stress relaxation measurements in glassy Zr52.5Ti5Cu17.9Ni14.6Al10 in the bulk and ribbon forms are presented. It is found that the density of bulk samples is higher than that of ribbon specimens while the stress relaxation kinetics are not much affected by a change of the quenching rate of four orders of magnitude. The kinetic relaxation law is determined. The stress relaxation depth is found to decrease sharply with the preannealing time. It is concluded that (i) stress relaxation occurs as a result of irreversible stress-oriented structural relaxation with distributed activation energies; (ii) the results obtained are inconsistent with the free volume as a source of elementary relaxation events; (iii) alternatively, the relaxation centers responsible for homogeneous flow may have properties similar to those of dumbbell interstitialcies in crystalline metals.