AE characteristics and recovery behaviors of tensile properties of neutron irradiated zirconium

The effects of fast neutron irradiation up to 4 x 1019 m/cm2 (E > 1MeV) upon the tensile properties and the acoustic emission (AE) characteristics of zirconium was investigated at room temperature. In the irradiated specimens, a number of AE signals which correspond to the formation of deformation twin are detected during the tensile deformation process. On the other hand, in the neutron irradiated specimens, the acoustic emission is extremely suppressed and the sharp yield point phenomenon is observed in the stress-strain curve. These results, therefore, indicate that deformation twinning can be suppressed by the neutron irradiation induced defects. The recovery behavior shows the good agreement with the recovery of the tensile properties and the AE characteristics due to the post-irradiation annealing. The AE parameters calculated by the amplitude distribution analysis showed the recovery behavior due to the post-irradiation annealing. The AE characteristics and the tensile properties almost recovered by the annealing at 6000C. The results indicate that the mechanism of fracture phenomena such as the stress corrosion cracking of neutron irradiated fuel cladding materials (Zircaloy) should be taken into account of the suppression effect of deformation twinning. The suppression of AE and the occurrence of the yield phenomenon were discussed in relation with the dislocation channeling observed by the transmission electron microscope. (author)