Mechanical properties of tungsten: Recent research on modified tungsten materials in Japan

There remain some drawbacks of mechanical properties of W materials as a plasma facing material (PFM) for fusion reactor divertors, which are low temperature brittleness, high ductile-to-brittle transition temperature (DBTT), and recrystallization-induced embrittlement. To solve these issues, development of W materials with improved thermo-mechanical properties, neutron irradiation tolerance, and possibility of mass-production with microstructural uniformity has been advanced for the last decade under the collaboration R&D by universities in Japan. In this paper, the effects of grain refining, K-doping, dispersion strengthening by La₂O₃ particles, and alloying by Re are discussed from the viewpoints of both short- and long-term material properties and phenomena, including effects of neutron irradiation and high heat loads, which should be considered under the actual fusion reactor environments. Through this R&D, K-doping and Re-addition showed several positive effects. Among the materials developed in this R&D, K-doped W-3%Re hot-rolled plate could be a better solution for PFM, which demonstrated superior properties from several perspectives. However, materials alloyed by Re have an intrinsic concern of higher irradiation hardening caused by neutron irradiation up to higher doses. Therefore, it is pointed out that investigations of thermo-mechanical properties under higher dose neutron irradiation are significantly required to realize long-term structural reliability and lifetime of fusion reactors.