Thermal stability of differently rolled pure tungsten plates in the temperature range from 1125°C to 1250°C

Application of rolled tungsten as armor of plasma-facing components in future fusion reactors requires its deformation-induced microstructure remaining stable during operation. At high operation temperatures, restoration processes as recovery, recrystallization and grain growth will unavoidably embrittle ductile tungsten achieved by rolling. Three pure tungsten plates manufactured by unidirectional rolling or cross-rolling in two different manners were qualified as baseline material for DEMO. To investigate their thermal stability, hardness testing is performed after isothermal annealing in the temperature range between 1125 °C to 1250 °C. The recrystallization kinetics of the different plates (and different regions within them) is analyzed thoroughly to allow extrapolation outside the investigated temperature range. Significant differences between the recrystallization kinetics of the three tungsten plates originate from the microstructure established by rolling. Two of the plates showed pronounced local differences in their recrystallization kinetics with the core of the plates recrystallizing ahead of the edge regions closest to the rolls. The third plate exhibits best thermal stability without notable differences between the local recrystallization kinetics. Where the two former plates may survive operation for two full power years only at temperatures less than 1005 °C, the later plate could sustain 1035 °C for the same period.