ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 18 and testing allow for the rapid assessment of new compositions of refractory, ceramic, or metallic HEAs specifically tailored for first-wall applications[17-19]. Figure 1 is a schematic that shows an example approach of such an acceler- ated materials discovery framework. The CHADWICK program has three projects aimed at the discovery of novel HEAs for fusion applications (Batch-wise improvement in reduced design space using a holistic optimization technique for fusion environments—led by Texas A&M Engineering Experiment Station; Refractory alloys with ductility and strength—led by Ames National Laboratory; and Design of complex high-performance armor materials—led by Lawrence Livermore National Laboratory)[16]. Grain Boundary Engineering. It is well established that the micro- structure of the material has a direct relationship with the performance of the bulk material. The grain boundaries of a polycrystalline material can be modified with different processing techniques to improve various bulk properties. Traditional metallurgy often employs techniques such as annealing and cold working to alter the density or orientation of the grain boundaries to increase strength and change ductility. Nanomaterials can surpass the conventional Hall-Petch relationship between grain size and strength by introducing very high interfacial energy into the grain boundary itself[20]. This can be achieved by locking in chemistry, structure, and phases through severe deformation or rapid quenching. In certain materials, amorphous phases are observed in the grain boundary that are expected to inhibit grain growth and function as strong neutral sinks for irradiation damage[21]. Figure 2 shows a schematic depicting the difference in materials’ ability to heal irradiation-induced defects between conventional coarse-grained and nanocrystalline materials[22]. The ability to consistently produce the amorphous grain boundary phases and maintain phase stability under high-temperature irradiation could make these materials especially suited for fusion first-wall applications. The CHADWICK program has two projects specifically aimed at creating, and stabilizing these amorphous grain boundaries, and validating their irradiation resistance (Complexion engineered nanocrystalline tungsten alloy plasma facing materials for longpulse tokamak operation—led by Johns Hopkins University; and Gradient composites with radiation amorphization- enabled dimensional stability and energy dissipation—led by University of Illinois, Urbana-Champaign)[16]. Geometrically Complex Systems. Existing tungsten plasma-facing armor is typically made of flat plates due to ease of fabrication and consistency. However, advancements in additive manufacturing make it possible to create complex geometries that enhance the performance of the component. Previous studies on plasma erosion showed that geometrically complex materials can significantly reduce plasma arcing and decrease the sputtering yield in comparison to a flat component[23]. Optimizing the component geometry in combination with other material advancements has the potential to dramatically increase the lifetime of plasma-facing components and reduce the need for maintenance and replace- ment of the first-wall component. The CHADWICK program has two projects exploring volumetrically complex geometries using advanced manufac- turing techniques to reduce plasma erosion in fusion power plants: (Combinatorial modeling, screening, and development of tungsten-ceramic composites with gradient microstructure for improved radiation-tolerant plasma-facing materials—led by the University of Kentucky; and Machine learning for alloy discovery coupled with geometric optimization for functionally graded liquid metal first wall—led by Savannah River National Laboratory[16]. Figure 3 shows a schematic of a typical microstructure of such composite material. Liquid Metal Alloys. An alternative design for the fusion first wall is to use liquid metal to achieve better heat transfer while eliminating issues related to tritium retention, irradiation damage, or structural failures. However, the implementation of liquid metal requires complex systems to ensure adequate flow rate and adhesion[24]. In addition, the potential vaporization of the liquid metal can have adverse effects on plasma purity and cause unintended Fig. 2 — Schematic showing (a) irradiation-induced defect formations in conventional materials, and (b) potential ability of nanocrystalline materials to annihilate irradiation-induced defects. (a) (b) Fig. 3 — Schematic illustration of a typical composite material microstructure.
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