The influences of deuterium irradiation defects on mechanical properties for ceramic breeder material Li₂TiO₃

Highlights: • The reduction of Vickerness hardness is caused by F-center defects in Li2TiO3 crystalline grains after deuterium irradiation. • F-center defects in crystalline grains will be aggregated to form defect clusters with the increase of heating temperature, which lead to a hardening tendency within a certain temperature range. • The aggregated defect clusters in the crystalline grains begin to recover when the annealing temperature increases to a point temperature, which results in the decrease of Vickers hardness. - Abstract: Tritium breeder materials are significant for blanket design of fusion reactor. However, during blanket operation, the ceramic breeder materials will be subject to neutron irradiation, which could be detrimental to mechanical properties. Because of good chemical stability and available tritium release behavior, Li₂TiO₃ is becoming one of candidate ceramic breeder materials. In this study, Li₂TiO₃ samples are irradiated by 120 keV deuterium ions. For sample characterization, the phase composition is investigated by X-ray diffraction (XRD) before and after irradiation. After deuterium irradiation, the Electron Spin Resonance (ESR) experiments are employed to investigate the irradiation defects. Micro-hardness measurement is applied to study the changes of mechanical properties. XRD results indicate that Li₂TiO₃ crystals are damaged by deuterium irradiation, but no new phases are produced. According to ESR experiment, the main defect type after deuterium irradiation is F-center which are vacancies trapping one electron. According to Vickers hardness measurement, size effect of micro-hardness is observed. The Meyer coefficient obtained in the experiment is 1.65, which is less than 2. Vickers hardness increases as applied loads decrease which are consistent with Meyer theory. And Vickers hardness of Li₂TiO₃ decreases as irradiation doses increase.