Stress Overshoot in Stress-Strain Curves of Zr<SUB>65</SUB>Al<SUB>10</SUB>Ni<SUB>10</SUB>Cu<SUB>15</SUB> Metallic Glass

Abstract

We have investigated the essential features of the stress overshoot in the stress-strain curves of a Zr 65 Al 10 Ni 10 Cu 15 (at %) metallic glass having a wide supercooled liquid region. The stress overshoot was observed in a non-Newtonian flow state appeared at higher strain rates and lower temperatures. The stress overshoot increased with decreasing temperature and increasing strain rate. Moreover, the stress overshoot appeared again after stress relaxation, which increased with the stress-relaxation fraction. A change in strain rate during plastic deformation, furthermore, gave rise to stress overshoot or undershoot which was sensitive to the increment in the strain-rate change. The stress overshoot seemed to be caused by an increase in atomic mobility with increasing strain rate (pseudoplasticity) and its change due to the yielding. The stress overshoot after the stress relaxation, moreover, appeared to be derived from the decrease in atomic mobility during the relaxation. In contrast to the non-Newtonian flow state, no stress overshoot was observed in a Newtonian flow state that was appeared at lower strain rates and higher temperatures in the supercooled liquid state because of no change in the atomic mobility.