Microstructure evolution and hardening of helium ion irradiated tungsten

Tungsten is a promising candidate material for plasma-facing components in future fusion reactors. An important issue is the irradiation-induced degradation of its mechanical properties and its typically superior thermal conductivity. In this study, tungsten was irradiated with 270 keV He+ to the damage levels of 0.7 dpa and 3.0 dpa at 500 degrees C and 800 degrees C. The overall distribution of the microstructure is observed and its evolutionary relationship with the micromechanics property is discussed. The study of the microstructure reveals that the increase in He (+) ion fluence leads to an increase in the density of bubbles, which conversely decreases with elevating temperature. Both 1/2 <111> and <100> loops have been identified in the current study, and 1/2 <111> loops will gradually transform into <100> loops as the temperature rises. The synergistic interaction between He bubbles and dislocation loops results in irradiation hardening, with the contribution of dislocation loops exceeding that of He bubbles. The increased presence of <100> loops at elevated temperatures further contributes to additional hardening increments. These findings help to understand the influence of bubble evolution and irradiation hardening behavior in tungsten, especially the contribution of different types of defects to hardening, and thus help to design new radiation resistant PFMs.