THERMALLY ACTIVATED DEFORMATION AND DYNAMIC STRAIN AGING OF Zr–4 ALLOY DURING STRESS RELAXATION

The thermally activated deformation and dynamic strain aging (DSA) of Zr–4 were investigated by stress relaxation experiments in a broad temperature range. It is found that in the process of stress relaxation, the plastic deformation rate of the alloy decreases with the relaxation
time, and this rate and the stress reduction ratio at the end of relaxation exhibit a minimum value at about 623 K. The activation volume associated with dislocation motion is found from the relationship between the stress and relaxation time. A noticeable maximum value appears around 623 K when the activation volume plotted against the temperature, which suggests that at this temperature, DSA is most pronounced. The strain ependence of the activation volume is analyzed. The rate controlling deformation mechanism is identified as the overcoming of solute atoms by dislocations, and the dislocation density is found to have an influence on DSA.