TEM, positron lifetime and hardness measurements of irradiated, cold-worked and annealed Zr-1%Nb

Tensile specimens of Zr-1%Nb plate were irradiated in Loviisa 1 NPP for one year during 1978-1979. The previous examinations with these specimens consisted of tensile tests at 24 °C and 280 °C. The results of some further studies with these specimens are presented in this report. Unirradiated Zr-1%Nb plate was used as a reference material. The defect structures present in the material after different treatments and the recovery of defects in thermal annealing were examined with transmission electron microscope (TEM) and by hardness and positron lifetime measurements. Four different treatment variations were included: recrystallized (unirradiated), irradiated, heavily cold-worked (unirradiated) and both irradiated and cold-worked. The TEM examinations showed high defect density both in the as-irradiated and in the cold-worked specimens. The as-irradiated specimen was assumed to contain mostly various types of point defects, whereas a dense dislocatior. network was present in the cold-worked specimens. Only slight (if any) change could be observed in the microstructure after one hour annealing at 400 °C. The recovery behaviour of the as-irradiated and cold-worked specimens found by the hardness and positron lifetime measurements were very close to each other. The measurements showed that the recovery occurred mainly at 450-550 °C. The results are compared to those presented in the literature for zirconium. Reference is also made to the results of the previous tensile tests.