Study on irradiation hardening by He+ and subsequent V/self-ion irradiation in V-4Cr-4Ti under near-service conditions

V-4Cr-4Ti was irradiated by He+ and subsequent V/self-ions at 773 K to simulate the effect of the damages generated under near-service conditions on irradiation hardening. Microstructure observation and hardness test were carried out by transmission electron microscopy (TEM) and nanoindentation testing. Microstructure analysis showed that bubbles, dislocation loops and precipitates were produced whether samples were irradiated by He+ or He+/V+. Edge dislocation was observed by high-resolution images. The nanoindentation results showed that hardening appeared after irradiation, and hardness increment after He+ irradiation is 4.41 GPa, 6.2 GPa for He+/V+. Meanwhile, based on damage characterization, the irradiation hardening was also analyzed using the dispersion barrier hardening model (DBH), which showed that the main cause of hardening was dislocation loops. In addition, the deviation was discussed between the hardness increment obtained by nanoindentation testing and that calculated based on DBH.