Irradiation creep of 3C-SiC and microstructural understanding of the underlying mechanisms

Irradiation-induced creep in high-purity silicon carbide was studied by an ion-irradiation method under various irradiation conditions. The tensioned surfaces of bent thin specimens were irradiated with 5.1 MeV Si2+ ions up to 3 dpa at 280-1200 °C, which is referred to as a single-ion experiment. Additional He+ ions were irradiated simultaneously in the dual-ion experiment to study the effects of transmuted helium on irradiation creep. Irradiation creep was observed above 400 °C in the single-ion case, where a linear relationship between irradiation creep and swelling (C/S) was observed at 400-800 °C for all stress levels (150, 225, and 300 MPa). The proportional constant of the C/S relationship was strongly dependent on temperature and stress. A rapid reduction in creep strain was observed above 1000 °C. On the basis of the microstructural analysis, anisotropic distribution of self-interstitial atom (SIA) clusters was suspected to be the primary creep mechanism. Some interesting results were obtained from re-irradiation under stress after the irradiation without stress. The creep strain was significantly retarded by pre-irradiation to even 0.01 dpa at 400 and 600 °C. This implies that the loop orientation was determined very early in the irradiation regime. For the dual-ion cases, irradiation creep was absent or very limited at all irradiation temperatures studied (400-800 °C). Microstructural analysis indicated that helium inhibited the stable growth of SIA clusters and prevented them from exhibiting anisotropic distribution.