Tailored irradiation resistant tungsten nanofoams

Owing to their excellent properties, tungsten (W)-based materials have become indispensable parts in fusion power plants. Facing the extreme radiation environments in emerging fusion reactors, conventional W-based materials experience severe microstructural changes and dramatic degradation of mechanical properties. The introduction of a very high density of free surfaces has been proven an effective method to improve a materials irradiance resistance. Therefore, the aim of this work is to design unique radiation tolerant materials based on nanoporous W structures. Due to their high surface fraction, irradiation should have little effect on the morphology and mechanical properties of the developed W nanofoams, in strong contrast to conventional bulk materials. To achieve this goal, a special scalable production route developed at the hosting institution-severe plastic deformation in combination with selective dissolution-will be employed to tailor nanoporous structured W, i.e., nanofoams on a bulk scale. The combination of in situ small scale testing and proton beam irradiation will be utilized for evaluation of the microstructure and nanoscale material properties to examine mechanical property changes induced by irradiation. Based on this, a physically based model accounting for the detailed elemental deformation and fracture mechanisms of these novel nanoporous materials will be derived. This work provides, for the first time, an innovative research concept to tailor W nanofoams that exhibit superior irradiation tolerance. Moreover, as developed experimental and theoretical concepts are generally applicable and can be transferred to other materials in the future, the results from the proposed project will serve as foundation for forthcoming related scientific studies and engineering applications.

Radiation damage is a factor determining the lifetime of numerous components of nuclear plants. Owing to their excellent properties, tungsten (W)-based materials have become indispensable parts in fusion power plants. Facing with the extreme radiation environments in emerging fusion reactors, however, conventional W-based materials experience severe microstructural modifications that alter their mechanical properties. The introduction of a very high density of free surfaces has been proven an effective method to improve a material's irradiation resistance. Therefore, the aim of this project was to design unique radiation tolerant materials based on nanoporous W structures. In this research project, synthesis of nanoporous W (i.e. W nanofoams) was achieved by a unique procedure involving severe plastic deformation of a coarse-grained tungsten-copper (W-Cu) composite followed by selective phase dissolution of the nobler Cu phase. The types of etching solutions turned out to have a significant impact on the surface diffusion characteristics of W atoms, thereby influencing the foam structures. Using nanoindentation and microcompression test in-situ in a scanning electron microscopy, we demonstrated that the W nanofoams, characterized by a network of interconnected nanocrystalline W ligaments and interconnected nanopores, possess outstanding strength. Moreover, the performance of the W nanofoams was unveiled to be highly dependent on the cellular architecture, including relative density, cell shape anisotropy, ligament thickness and structural disorder. The unique fabrication route of W nanofoams developed in this work is generally applicable to other attractive nanoporous active metals, which are difficult to obtain using a classical electrochemical dealloying approach. Our knowledge regarding the effect of etching solutions can be used to tailor porous W materials with various structural parameters. The findings on how structural details influence the mechanical performance of metallic foams provide valuable structural optimization guides for producing cellular solids with specific end-use properties. The promising mechanical results of nanoporous W will serve as a foundation for forthcoming related scientific studies and engineering applications. The created nanoporous W itself serves a model for promoting our basic understanding of foam responses in an extreme radiation environment.