Fracture surfaces of tungsten wires used in fiber-reinforced plasma facing components: Effect of potassium doping and high temperature annealing

摘要

We have studied the microstructure of tungsten fibers, which are considered as reinforcement elements for the advanced tungsten composites (W-f/W) known to exhibit pseudo ductile behaviour at room temperature. The potentially negative impact of the high temperature annealing, expected under operation in fusion environment, remains to be explored and mitigated. Doping by potassium is considered as a main option to delay recrystallization and grain growth inside the drawn tungsten wires to a higher temperature. Here, we have performed a systematic analysis of the fracture surface of pure and K-doped tungsten wires which were annealed prior to a uniaxial tensile test. The results demonstrate that the fracture mechanism depends strongly on the annealing temperature and presence of potassium doping. Four fracture mechanisms were clearly distinguished and classified by converting into deformation maps as a function of annealing and test temperature. By summarizing all previously available results and current ones, one can demonstrate that potassium doping delays massive grain growth (and subsequent loss of strength) by similar to 600 degrees C as compared to the pure W wire and this positive effect holds for the deformation not only at room temperature but at least up to 500 degrees C.