Radiation-induced void formation and ordering in Ta-W alloys

We have assessed the formation and evolution of void and dislocation arrangements in Ta, Ta-5wt.%W and Ta-10wt.%W as a function of radiation level at a temperature of 345 ± 3 °C, by combining proton irradiation experiments, transmission electron microscopy and nano-hardness measurements. The damaged structure of tantalum at 0.1 dpa is characterized by the presence of a/2 〈111〉 interstitial dislocation loops and randomly distributed voids, whereas only dislocation loops are observed in the two alloys. Void ordering occurs in tantalum at 0.25 dpa, together with the appearance of dense dislocation tangles. A further increase in damage level leads to a continuous nucleation and growth of voids, and saturation is not attained at a damage level of 1.55 dpa. In contrast, the average size and number density of dislocation loops increases gradually with damage level in the two alloys, and voids only form at 1.55 dpa. Tungsten delays the loop evolution and therefore the formation of radiation-induced voids.