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

Abstract

We have studied the microstructure of tungsten fibers, which are considered as reinforcement elements for the advanced tungsten composites (Wf/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 testing 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 ~600°C as compared to the pure W wire and this positive effect holds for the deformation not only at room temperature by at least up to 500°C.

Recent progress in the assessment of irradiation effects for in-vessel fusion materials: tungsten and copper alloys

“…The fracture surface of the tested samples was inspected by SEM using the same methodology as earlier applied in [29]. The conclusion on the prevailing type of the microstructure was based on the detailed inspection of three to five zones for each test condition.…”

EBSD characterization of pure and K-doped tungsten fibers annealed at different temperatures

“…Potassium doping has already proved its efficiency on suppressing secondary recrystallization and controlling grain growth up to 1900°C in tungsten thin wires [26][27][28]. Although these materials have been characterized in terms of microstructure, texture and mechanical behavior [26][27][28][29][30][31][32][33][34], a dedicated study on the role of both triple junction and grain boundary character distributions is still missing. The main goal of this paper is to assess potential anisotropy in the material and to compare the evolution of both distributions in pure and K-doped W fibers annealed at different temperatures.…”

Toughen and Strengthen Alginate Fiber by Incorporation of Polyethylene Glycol Grafted Cellulose Nanocrystals

“…There were more and more irregular zigzag stripes on the fractured cross-section of modi ed alginate bers. This was the main feature of the matrix's transformation from brittleness to plastic deformation (Terentyev et al 2019), indicating that the ability of modi ed ber to resist crack propagation had been improved.…”