Improvement of surface exfoliation behavior by helium-ion bombardment of a tungsten alloy fabricated by mechanical alloying

Blistering and exfoliation of several tungsten alloys, which cause surface damage, were investigated using 3-MeV He-ion bombardment at room temperature (RT), 400, and 550°C. The alloy W-0.3T1C, which was fabricated by the mechanical alloying method and had an ultrafine grain structure, a K-doped W alloy, and pure W metal were examined to explore a way of suppressing the surface damage. In RT irradiation, surface exfoliation occurred at a fluence of (1-2) × 10²²He/m² in all the tested specimens. In the case of 550°C irradiation, surface exfoliation was observed above 2 × 10²²He/m²irradiation in pure W and K-doped W, but no surface exfoliation was observed in W-0.3TiC up to a fluence of 2 × 10²³He/m². The results showed that W-0.3TiC showed a higher resistance to surface exfoliation by He-ion bombardment and the level of resistance was temperature-dependent. The surface morphology, cross-sectional morphology, and microstructure were characterized by transmission electron microscopy. Helium thermal desorption spectrometry was carried out to determine the mechanism whereby the surface attained resistance to the damage through He-ion bombardment. The improvement in the resistance to the surface exfoliation could be attributed to the ultrafine grain structure and the intergranular enhanced He diffusion behavior of the MA-processed material.