ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 19 shutdowns. New liquid metals with low vapor pressure, low melting point, and minimal plasma contamination could mitigate many challenges associated with implementing a liquid metal first wall. The CHADWICK program has funded one project to increase the feasibility of using liquid metal as a fusion first wall (Novel liquid metal plasma facing component alloys—led by ExoFusion)[16]. Materials Testing and Validation. Materials testing and qualification methods to validate performance are typically established by the American Society of Mechanical Engineers (ASME) and ASTM International. Depending on the material being tested, commercially available standards may be employed to validate the thermal and mechanical performance of the newly discovered material[25,26]. For irradiation and plasma testing, there are no existing commercial standards that can be referenced to ensure consistency. The CHADWICK program has involved capability teams to independently validate irradiation and plasma resistance of the developed material product (High flux plasma- materials interaction testing for rapid fusion materials development— led by the University of California San Diego)[16]. The Plasma Interaction with Surface Component Experimental Station (PISCES) facility developed by this team will aid teams in testing how new materials will react to the plasma and irradiation environment expected in a fusion power plant. Every project that makes advancements in their approach will be able to share their public data in a centralized open-source database for independent techno- economic and activation assessment (Centralized and on-demand radiation transport and techno-economics for fusion material engineering—led by University of Illinois, Urbana-Champaign)[16]. Material advancements that can demonstrate concrete cost savings could be further developed into specifi- cations passed to manufacturers to sell as a commercial product. In addition to the development of new materials, the establishment of new validation and verification methods for fusion materials will also be an end product of this program. Fabrication and Joining. Any new material developed for the first wall will need to be fabricated and joined to meet the performance and quality requirements of the fusion power plant. Dissimilar metal welds between high-temperature materials have traditionally been difficult to make and can act as initiation sites for failure. The transition layer and heat-affected zone of these welds could cause the formation of undesirable phases[27]. The difference in the coefficient of thermal expansion at the interface of dissimilar metals can also increase the residual stress of the weld and the likelihood of cracking. Depending on the base material and weld material selected, additional weld processing steps may be necessary to reduce porosity, phase instability, cold cracking, hot cracking, or solidification cracking[28]. Such processing may be infeasible for certain component geometries or sizes. Given these uncertainties, co-development of the first-wall component along with the materials and weld process is needed to mitigate the risk of weld failure. The CHADWICK program has funded two projects specifically aimed at co-developing welding or friction stir processing alongside fusion power plant design (Co-optimization of an integral, layered materials solution for compact tokamak vessels—led by Commonwealth Fusion Systems; and Ferritic and vanadium alloys with nanoparticle strengthening for fusion— led by Pacific Northwest National Laboratory) and one project focused on development of monolithic platelet/continuous fibrous ultra-high temperature ceramic composites (Design and development of composited low- activation UHTC materials for very high temperature first-wall application—led by Stony Brook University) to ensure complex systems can be fabricated reliably[16]. SUMMARY ARPA-E’s CHADWICK program seeks to accelerate the discovery of new materials that can endure the extreme conditions in commercial fusion reactors. This article discussed key challenges in fusion first-wall design—such as irradiation hardening, segregation, swelling, creep, helium embrittlement, and plasma erosion— and how these issues demand novel structural and plasma-facing materials. The CHADWICK program addresses these needs by funding projects targeting high entropy alloys, engineered grain boundaries, complex additive- manufactured geometries, liquid metals, and advanced validation methods. Through close coordination of materials design, testing, and fabrication, the program aspires to deliver next-generation, first-wall materials that meet stringent requirements for commercial fusion viability. In addition to the development of new materials, the establishment of new validation and verification methods for fusion materials will also be an end product of this program. Disclaimer: The vision of the program was developed by the ARPA-E program director Ahmed Diallo. This publication is for informational purposes only, its content may be based on employees’ research and does not represent the position or opinion of Booz Allen. Furthermore, Booz Allen disclaims all warranties in the articles’ content, does not recommend/endorse anything referenced therein, and any reliance and use of the articles is at the reader’s sole discretion and risk. The author’s affiliation with The MITRE Corporation is provided for identification purposes only and is not intended to convey or imply MITRE's concurrence with, or support for, the positions, opinions, or viewpoints expressed by the author. This article was developed by authors 1 and 2 under contract number 89703024DAR000002 with Booz Allen Hamilton to the U.S. Department of Energy’s Advanced Research Projects Agency-Energy. ~AM&P For more information: Cheng Xu, principal nuclear engineer, MITRE Corp., cxu@mitre.org; Pankaj Trivedi,
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