[en] The effect of the annealing temperature on the microstructure and grain boundary character distribution of potassium doped tungsten fibers made of drawn wire was investigated by Electron Backscatter Diffraction. Samples, with a diameter of 148.7 μm, in the as-received condition and annealed at 1300, 1600, 1900, 2100 and 2300 °C were analyzed at the center of the transversal sections. Up to 1900 °C, a uniform microstructural coarsening and primary recrystallization followed by normal grain growth was observed. Between 1900 and 2100 °C abnormal grain growth took place. The strong texture (<110> parallel to the drawing axis) remained present in all conditions. With increasing the annealing temperature, the low angle grain boundary fraction increased at the expense of high angle grain boundaries while the amount of coincidence site lattice boundaries reached its maximum at 1600 °C. At this temperature, the most resistant configuration of triple junctions against intergranular crack propagation was obtained. (paper)

[en] Highlights: • Microstructure of ITER-specification tungsten is investigated. • Recovery occurs at 1300 °C and recrystallization between 1300 and 1500 °C. • Increasing annealing temperature strengthens deformation texture. - Abstract: Tungsten and its alloys have been extensively studied to be used as materials for plasma facing components (PFCs) in future nuclear fusion reactors. Under fusion operating conditions, the surface of PFCs will experience high heat flux exposure which will affect some microstructural features of the material. In the present work, the effect of annealing temperature on microstructure, texture and mechanical behavior of ITER-specification commercial pure tungsten was investigated by combining Electron Backscatter Diffraction (EBSD), Vickers micro-hardness and nano-indentation techniques. The samples were analyzed in the as-received and in the annealed conditions. Annealing was done for 1 h at three different temperatures: 1300 °C, 1500 °C and 1800 °C. Three stages in microstructural evolution were observed: recovery at 1300 °C, recrystallization at 1500 °C and grain growth at 1800 °C. As the annealing temperature increases and recrystallization takes place, α-fiber texture components are strengthened. Simultaneously, a reduction in both Vickers and nano-indentation hardness is found.

[en] Highlights: • ITER specification tungsten is studied under plastic deformation • Plastic deformation suppresses He retention • He exposure strongly affects sub-surface microstructure - Abstract: The retention of deuterium (D) and helium (He) is studied in pure tungsten after high flux mono-plasma exposure. The recrystallized and plastically deformed tungsten samples are studied to clarify the impact of the material microstructure, in particular dislocation density, on the trapping and release of D and He. Thermal Desorption Spectroscopy (TDS) measurements are performed to reveal the release stages and quantify the retention. Preliminary transmission electron microscopy study was applied to clarify the microstructural modifications induced by the plasma exposure to support the discussion and conclusions. It has been demonstrated that plastic deformation causes considerable suppression of He release within the explored limit of the TDS temperature – 1300 K. This is opposite to what is found for the pure D exposure, where the plastic deformation evidently enhances the D retention, given equivalent exposure conditions in terms of surface temperature and ion fluence.