Atomic and Microstructural Evolution of Mixed Spectrum Neutron-Irradiated Tungsten Alloys: Insights From Multimodal X-Ray Spectroscopy and Diffraction Characterization
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Tungsten is currently the leading candidate material for plasma-facing applications in fusion devices due to its high melting point and resistance to sputtering. However, its long-term stability is a concern as exposure to neutrons degrades mechanical properties. While high-fluence conditions with large Re and Os transmutation concentrations are known to cause embrittlement, the effects of lower fluence on microstructure and property evolution are less explored. In this study, we use X-ray Absorption Spectroscopy (XAS) and high-energy X-ray Diffraction (XRD) to quantify the atomic and microstructural properties of unirradiated and neutron-irradiated tungsten alloys. The alloys studied include single crystal W, polycrystalline W, K-doped W, W-3%Re, K-doped W-3%Re, and La-doped W-3%Re. Specimens were neutron-irradiated at 850°C and ~ 1100°C to ~ 0.5 displacement per atom. Our XAS results revealed multiple differences in the atomic environment across the W-alloy matrix. These differences were alloy-dependent and varied with irradiation temperature. After 850°C, non-body-centered cubic (BCC) Re and Os components were found with χ phase (Re 3 Os) and hexagonally close packed structures. After 1100°C, the final Re atomic structures were alloy-dependent, with Laves phase (Re 2 W), and χ-phase (Re 3 Os and Re 3 W) intermetallic environments quantified, while Os atoms were found in a body centered cubic and hexagonally close packed environments. XRD results indicated alloy-specific microstructural stability, with Re-La-W and Re-K-W alloys showing the least lattice swelling and lowest two-dimensional defect concentrations, while pure-W specimens show the highest irradiation-induced lattice expansions and two-dimensional defects. Understanding these early-stage evolutions is crucial for developing strategies to mitigate late-stage precipitation effects through alloy design.
