Development of Ultra-Fine Grained Tungsten Alloys for Fusion Rector Applications Topic - Advancing Technologies and Materials for Fusion Energy Systems, Subtopic - Plasma Facing Components

Tungsten is a leading candidate material for plasma facing components in current fusion reactor designs. It has the highest melting point of any pure metal and it has good thermal conductivity, although questions remain concerning tungsten’s interactions with high temperature plasmas, as well as issues with its ductility and fracture toughness. The latter mechanical properties related to ductility require focused attention, particularly in applications experiencing cyclic thermal loading and high thermal gradients, both spatial and temporal. This proposal centers on a novel low cost powder metallurgy process to produce ultra-­‐fine grain W alloys with high density. Powder metallurgy tungsten and tungsten with minor alloying additions have been produced that have achieved high density, normally exceeding 98 % and some samples exceeding 99 %. The process has also attained grain sizes as low as 200 nm. The minor alloying of tungsten can contribute to ductility through solution the matrix or aid in grain boundary pinning, and therefore reduce grain growth during sintering. Alloys of many materials with ultra-­‐fine and nano-­‐sized grains are exhibiting a range of properties not seen in their larger grained counterparts, including improved strength and fracture toughness. While testing of such ultra-­‐fine grain tungsten alloys has shown lowered blistering response in plasma environments, investigation of the level of mechanical property improvement under thermally induced stresses is needed. Phase I of this project will formulate a range of W alloy compositions, including the promising tungsten plus molybdenum alloy, and test these materials for potentially lowered ductile-­‐to-­‐brittle transition temperature by using elevated temperature 3-­‐point bend testing, as well as potential improvements in high temperature ductility overall. Additionally, an apparatus will be designed that will be able to reproducibly subject samples under controlled atmosphere to cyclic thermal loading and thermal shock, thus allowing direct comparison of the most promising tungsten alloys for plasma facing components. Successful completion of this work holds the potential to significantly move tungsten materials toward practical application in fusion reactors.