Annealing effect on the microstructure of tungsten irradiated in SINQ target

In this work, the microstructure of pure tungsten irradiated in a target of the Swiss spallation neutron source is studied. The tested tungsten specimens were irradiated to two doses of 1.4 and 3.5 ddpa with 37 and 140 appm He at 80 and 110 °C, respectively. The specimen of 1.4 dpa was consecutively annealed at temperatures of 500 °C, 600 °C, 800 °C and 900 °C, for 1 h, and the post-irradiation annealing effect on the microstructure was investigated. Microstructural features such as dislocations, defect clusters, dislocation loops and bubbles were observed by means of transmission electron microscopy (TEM). TEM images were obtained in different areas of the samples, to obtain quantitative information of the dislocations and defect clusters. There was a significant change in the microstructure of the tungsten after irradiation and post-irradiation annealing. The average dislocation density and defect cluster density were evaluated.