Thermal stability of tungsten fiber-reinforced tungsten composites fabricated by powder metallurgy

• Two types of tungsten fiber-reinforced tungsten composites from powder metallurgy • First long-term thermal stability analysis at high temperature (2 weeks at 1450°C) • Recrystallization of fiber commences rapidly at rim and completes within a day • Grains in dense matrix coarsen and intergrowth with fibers occurs for longer times • No intergrowth of porous matrix and fibers, but loss of mechanical integrity Tungsten-based materials are considered as armor of plasma-facing components for future fusion reactors. To mitigate the brittleness of tungsten, tungsten fiber-reinforced tungsten composites (W f /W) have been developed. Two types of W f /W composites, with either continuous, aligned, potassium-doped tungsten wires in a dense tungsten matrix or randomly oriented, short fibers in a porous tungsten matrix are investigated. Both were fabricated using a powder metallurgical route facilitating field assisted sintering technology (FAST). Specimens are annealed at 1450 °C for different amounts of time up to two weeks to assess the thermal stability of the composites. Scanning electron microscopy and electron backscatter diffraction reveal major changes in the microstructure. After 4 hours of annealing initiation of recrystallization in the fibers concurrent to grain growth in the matrix is observed in both composites. Recrystallization commences at the outskirts of the fibers causing formation of a rim of small, recrystallized grains. Longer annealing increases the rim of recrystallized grains inwards into the fiber. After 3 days of annealing, all fibers are completely recrystallized, and the matrix is coarsened significantly by grain growth. While the short fibers can still be identified in the porous matrix after one week of annealing, matrix and continuous fibers cannot be distinguished any longer in the dense matrix. Short fibers with large, recrystallized grains can still be recognized after 2 weeks of annealing, while the porous matrix disintegrates by particle coarsening.