Superplastic characteristics and microstructure of neutron irradiated 3Y-TZP

Fast neutrons (energy > 1.6 x 10-13 J) were irradiated to 3Y-TZP specimens, typical superplastic ceramics, at the fluence of 2.5 x 1024 and 4.3 x 1024 m-2 at JMTR of JAEA. The Vickers hardness with indentation load of 4.9 and 9.8 N at room temperature was seemed to be slightly increased by the irradiation. Through the superplastic tensile tests in a temperature range from 1623 to 1773 K with initial strain rates of 5.0 x 10-4 and 1.0 x 10-3 s-1, it was found that the superplastic flow stress is decreased with increasing the neutron fluence. The microstructural features of the fractured specimens were observed by a SEM. It implies that the grain boundary microstructure of the irradiated specimens would be changed by annealing in the superplastic tests are elevated temperatures. It is quite probable that the irradiation-induced vacancy clusters might play an important role to weaken the grain boundary cohesion which may be an important factor to determine the superplastic properties, and hence they would decrease the superplastic flow stress. (author)