Microstructural and compositional effects of transition metal carbide additions on dispersion-strengthened tungsten fabricated via spark plasma sintering

Abstract

Tungsten is the plasma-facing material of choice for the divertor region in ITER as it has favorable properties under ion irradiation. However, tungsten is a very brittle material whose fabrication is complicated by its high melting point and low recrystallization temperature. Spark plasma sintering is a powder consolidation technique that can rapidly compact tungsten powder to high relative densities while preserving fine grain sizes. Dispersing fine transition metal carbide particles within the tungsten matrix has been proposed to enhance the ductility of tungsten by re-arranging the impurity distribution. Tungsten samples consolidated with 0.5–10 wt% zirconium carbide, titanium carbide, or tantalum carbide have been fabricated via spark plasma sintering to >90% relative density. Consolidated samples have transition metal-rich dispersoids uniformly distributed at grain boundaries and within the micron-sized tungsten grains. The presence of the dispersed second phase particles successfully refined the final grain size, as the average grain size decreased from 11 μm for the pure W samples to ~1 μm for the samples with 10 wt% second phase. Correspondingly, the hardness as measured via Vickers hardness rises as the grain size decreases and volume fraction of the second phase increases. XRD and XPS analyses show that formation of tungsten carbide and transition metal oxide complexes alter the impurity distribution and material performance.