Synthesis, characterization, and properties of carbide dispersion-strengthened tungsten alloys for use as a plasma-facing material in nuclear fusion reactors

Tungsten is the material of choice for plasma-facing components in future plasma-burning fusion reactors because of its high melting point, high sputter threshold, and low hydrogenic species retention. However, tungsten is an intrinsically brittle material, displaying no room temperature ductility and only exhibiting non-brittle failure at temperatures above 400 C. In addition to its limited ductility, tungsten’s high melting point and low recrystallization temperature pose complications during fabrication. Traditional synthesis routes tend to result in non-fully dense samples with coarse-grained microstructures. As a consequence, there is a desire for a fine-grained, fully-dense tungsten material that exhibits enhanced ductility. Tungsten is embrittled by impurity oxygen atoms residing at grain boundaries. It is theorized that by microalloying tungsten with transition metal carbides that capture the oxygen atoms, the impurity distribution can be altered to beneficially impact the mechanical properties. Through the advent of advanced powder processing techniques such as Spark plasma sintering, dense, fine-grained tungsten samples can be developed with these microalloyed microstructures. Spark plasma sintering is a powder compaction technique that provides high pressure and heating rates, allowing for a lower final temperature and hold time for compaction. In SPS, a strong electrical current is fed through the powder and die to heat the powder. An applied uniaxial force combines to compress the powder to a solid compact, leading to fully dense materials at lower temperatures as compared to conventional sintering. In this work, spark plasma sintering is employed to develop tungsten materials alloyed with tantalum carbide, titanium carbide, or zirconium carbide. Samples are fabricated with varying compositions of added carbides (from 0.5-10 wt.%), and the sintering process results in >90% dense samples with grains