Thermally activated deformation of Zircaloy-4

Tensile tests were carried out on Zircaloy-4 over the temperature range 298-798 K. Yield stress values at the strain rates 1.33x10-4 s-1 and 6.67x10-4 s-1 were used to determine the activation parameters. A peak in activation volume (Vsub(app)=3100 b3) was observed at about 690 K; outside this temperature range the activation volumes became almost independent of temperature (Vsub(app)=200-300 b3). The peak in activation volume was explained in terms of a basic rate controlling mechanism and dynamic strain aging. This analysis indicated that the peak could be ascribed to the negative value of the strain rate sensitive solute strengthening term M and that the mechanism based on the non-conservative motion of jogs appeared to be more favored as the basic rate controlling mechanism of Zircaloy-4 than an impurity mechanism. (orig.)