Doppler broadening spectroscopy was performed using a variable-energy positron beam to investigate the effect of defects induced by 150-keV Ar-ion-irradiated α-Zr bulk material. S parameter in the damaged layer of the as-irradiated sample induced by ion irradiation increased with the increasing implantation dose. Isochronal annealing between 350 and 800 °C in vacuum studies was carried out to investigate the thermal stability of defects in the oxide surface and damaged layer for low-dose (1×1014 cm2) and high-dose (1×1016 cm2) irradiated samples. The results of S-W plot measured at different annealing temperatures showed that the positron-trapping center had changed. The Ar-decorated voids or vacancies, which formed in high-dose implantation samples by Ar ions combining with open-volume defects, are stable and do not recover until at high annealing temperatures. Comparing the annealing behavior of the high-dose and low-dose implantation samples show that the recovery process of open-volume defects such as vacancies and voids will be delayed by the excess Ar concentration.