Changes in the microstructure and mechanical properties of Ti-6Al-4V alloys induced by Fe ion irradiation at a high He generation rate

As an attractive candidate structural material for nuclear applications, the irradiation resistance of high strength double-phase titanium alloys Ti-6Al-4V has received great attention. In this study, the damage dose dependence of defect evolution and hardening behavior at a high He generation rate (95 appm/dpa) for the Ti-6Al-4V alloys were investigated by TEM and nanoindentation. The Ti-6Al-4V specimen was pre-implanted with He ions with multi-energy at ambient temperature and subsequently irradiated with Fe ions at about 420 degrees C to obtain a He/ dpa plateau region (400-1000 nm) with average damage doses of 1.5, 7.5 and 37.5 dpa. TEM observations show that the bubble density showed a strong damage dose dependence. When irradiated to 37.5 dpa, the bubble exhibited a bimodal size distribution with the critical radius of approximately 1 nm. Meanwhile, the precipitate length showed an increasing trend with increasing depth, which is due to the effect of injected-Fe ions rather than the damage dose. In addition, no He dependence was observed for the loops and the precipitates. Nano -indentation results indicate that the irradiation hardening became more significant with the increase of damage dose. The contribution of irradiation-induced defects to the hardening was estimated by dispersed barrier -hardening (DBH) model.