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

Abstract

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 °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. Nanoindentation 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.