Computational Materials Design of Functionally Graded Structures for Enhanced Cooling of Plasma Facing Components via Additive Manufacturing

Plasma facing components (PFCs) in future fusion power plants will be subjected to a concentrated flux of plasma particles resulting in very high surface erosion and heat loads. The material most suitable to withstand these extreme loading conditions is tungsten (W) due to its excellent thermal stability and having the highest melting point of the metals. The drawback of tungsten is its brittleness at low temperatures making it necessary to join W to other materials that can provide mechanical support and active cooling, e.g. reduced activation ferritic martensitic (RAFM) steel used in next-generation helium-cooled fusion reactor designs. Traditional joining methods such as brazing or diffusion bonding create a sharp interface between the two materials, resulting in large thermal stresses that can lead to cracking or failure of the joint. Grading the materials to create a gradual joint can reduce the thermal stresses and improve joint reliability. Additive Manufacturing (AM) techniques, in which structures can be built layer-by-layer, provides a new and exciting method for creating functionally graded material (FGM) structures. Directed energy deposition (DED)- based AM techniques provide a robust, affordable, and technologically viable solution for producing functionally graded materials in flexible geometries. Under this STTR program, QuesTek Innovations LLC, a leader in the field of Integrated Computational Materials Engineering (ICME), will apply its computational materials design methodologies to design and fabricate a functionally graded material (FGM) component, joining the W shielding layer and underlying cooling structures (e.g., RAFM steel) via advanced Additive Manufacturing techniques for enhanced cooling of PFCs. The Phase I program will focus on utilizing ICME models and tools to identify an optimized composition path from W to RAFM steel that avoids formation of deleterious phases, optimizes solidification behavior, and minimizes coefficient of thermal expansion (CTE) mismatch along the gradient to produce a robust joint structure. QuesTek will utilize its expertise in computational thermodynamics, implementing thermodynamic models to calculate cracking susceptibility during AM processing, material CTE, and phase stability at equilibrium and non-equilibrium (rapid solidification) conditions across a full range of compositions in the FGM system of interest. With the input of these modeling results, academic partners at Texas A&M University (TAMU) will leverage their previously-developed path planning and optimization algorithm to determine optimized composition pathways. Upon identification of processing- and property-optimized paths, collaborators TAMU will use their multi-feeder Laser Engineering Net Shaping (LENS®) AM system to prototype W-RAFM steel FGMs and conduct microstructure/property characterization on the builds to validate the FGM designs. The framework developed under the proposed Phase I program for designing and printing functionally graded joints of highly dissimilar metals can be extended to include additional layers or materials of interest within the fusion reactor or even to components for other extreme environments with the need for advanced cooling, such as hypersonics, spacecraft thermal control systems, or energy recovery structures.