To study the effects of varying temperature on microstructural evolution, Fe-Cr-Ni austenitic model alloy was irradiated with 4 MeV Cu ions at constant temperatures of 473, 573, 773 K and stepwise temperature variation of 473/773, 573/773 K. Preirradiation at lower temperatures increased interstitial loop density in the subsequent irradiation at higher temperature, even if the dose of the former irradiation was low. However, most of the interstitial loops formed at 473 K or 573 K disappeared in the second step irradiation at 773 K. This phenomenon is not thought to be the result of thermal annealing but believed to be caused by reaction of defects or defect clusters formed at both lower temperature and higher temperature. A defect clustering model for interstitials and vacancies during irradiation indicates that the resolution of small vacancy clusters causes unexpected vacancy-rich condition temporarily in the case of temperature-variant irradiation.
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