Annealing of defect clusters in irradiated tungsten

Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in tungsten irradiated at reactor ambient tempeaature, ～ 70°C. Annealing, consisting of the growth and eventual elimination of the clusters, is observed to occur in two stages, one at temperatures below 435°C and one at temperatures above 740°C, which are interpreted as being due to interstitial and vacancy migration, respectively. The changes in defect cluster size and density are paralleled by similar changes in the measured strength of the material, and can be quantitatively correlated with the shear stress on the basis of a model of dislocation movement through a random array of obstacles.