Effect of annealing on microstructure, texture and hardness of ITER-specification tungsten analyzed by EBSD, vickers micro-hardness and nano-indentation techniques

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.