Materials challenges for the fusion nuclear science facility

•The FNSF materials strategy must bridge the gap between ITER and DEMO.•Advanced materials beyond pure tungsten are needed for the first wall and divertor.•Starting with a Gen-1 RAFM blanket, advanced alloys will be progressively introduced.•SiC flow channel inserts meet many requirements but require more development.•The vacuum vessel receives a low dose but must last the full device lifetime. The phased development and component testing mission of the Fusion Nuclear Science Facility (FNSF) implies a unique scenario for the development of structural and plasma-facing materials. The phased development of the machine and the capability to periodically remove and replace power core sectors allows for the introduction of materials and components with progressively improved operating characteristics throughout the lifetime of the machine. In addition, the machine components removed at each operational phase will provide the first opportunity to test and examine materials irradiated to useful neutron fluences in a fully integrated fusion environment. Options for structural and plasma-facing materials are considered and a preliminary set of materials identified to meet the challenges of power core components and for the machine-lifetime components such as the vacuum vessel and the structural ring. The status of FNSF-relevant materials research and development within the US fusion material program is summarized, and future directions for developing advanced materials to enable the long-term missions of an FNSF are discussed.