ULTRAMET — Department of Energy SBIR Phase II: Designs for the International Thermonuclear Experimental Reactor (ITER) employ several pla

Description

Designs for the International Thermonuclear Experimental Reactor (ITER) employ several plasma-facing materials selected for their suitability to regions of the vessel with different power and flux characteristics. Tungsten is one of the most important candidates for diverter component materials, given its low erosion and good mechanical properties at high temperature. However, high-toughness tungsten alloys that are suitable for fusion plasma environments still must be developed to overcome the inherently brittle nature of tungsten. Solid solution alloys of tungsten-iron with relatively high toughness and ductility, produced using chemical vapor deposition (CVD) processing, are being d eveloped. The process allows the direct deposition of solid solution alloys to produce complex net-shaped plasma-facing com ponents of the desired tungsten alloys, without the high impurity levels, porosity, complexity, and cost associated with alternative processing such as melting, sintering of powders, or homogenization heat treatments. CVD processing was successfully developed for a fully dense, uniform tungsten-iron (W -Fe) alloy that demonstrated increased ductility compared with pure tungsten. Alloys containing 2.5, 3.5, and 4.1 at% iron were produced. Nanoindentation testing showed the Young & apos;s modulus and hardness of the CVD W -Fe alloys were less than those values for CVD tungsten, and the W -Fe alloys survived multiple heating cycles to 1200C at a heating rate of 20C/sec. Dislocation motion in tungsten and W -Fe alloys was modeled u sing three complementary approaches: molecular dynamics, quantum m echanics, and kink pair nucleation and motion coupled with the phonon drag kinetic theory of gases. The CVD tungsten-iron solid solution alloys will be optimized, and detailed modeling and material characterization will be p erform ed. Specimens will be exposed to simulated plasma transients to characterize performance. High temperature thermomechanical properties (tensile and compressive strength vs. strain between ambient and 1200C) will be measured. Thermomechanical damage will be modeled using thermo-elasto- plasticity finite element modeling. Dislocation dynamics modeling of the plastic deformation of W -Fe alloys, and modeling of dislocation nucleation, emission, and motion from crack tips in tungsten and W -Fe alloys, will be performed to determine the influence of iron on the ductile-to-brittle transition temperature. Commercial applications and other benefits: Nuclear fusion is an ideal alternative to increasingly scarce and expensive fossil fuels and can provide a much greater quantity of environmentally sound energy than wind, solar, and geothermal sources. Practical application of fusion for efficient electricity generation requires the development of materials and structures that can withstand the demanding reactor environment. The proposed tungsten alloys are key materials for reactors that will ultimately be scaled up for commercial use.