PNNL

The Science   

Tungsten heavy alloys (WHAs) are promising candidates for plasma-facing materials inside fusion reactors due to their high strength and ductility. However, determining the material’s ability to withstand the extreme environments inside a fusion reactor necessitates dedicated evaluation and stress-testing. 

To address this issue, researchers at Pacific Northwest National Laboratory performed a quantitative assessment of a WHA comprised of 90% tungsten, 7% nickel, and 3% iron (90W-7Ni-3Fe) under simulated fusion reaction conditions. Using specialized microstructural evaluation techniques and a novel multi-projection scanning transmission electron microscopy (STEM) technique to evaluate interfacial damage densities, they characterized the resulting damage from high temperature irradiation, observing and quantifying significant cavity segregation along the interphase boundaries due to irradiation.

The Impact

WHAs can potentially serve as plasma-facing materials inside fusion reactors. However, more research is needed to characterize the effects of extended exposure to the fusion environment on the overall performance of the material. This study revealed microstructural changes to a WHA following ion irradiation. The formation and growth of cavities at the interphase boundary of the WHA observed in this research is anticipated to adversely affect the material’s toughness. This work reveals a pressing need for mechanical property testing of irradiated W–Ni-Fe dual-phase alloys to determine their suitability as plasma-facing materials.

Summary

Researchers characterized the microstructures of a 90W-7Ni-3Fe WHA using transmission electron microscopy (TEM). The material was sequentially Ni⁺ and He⁺ ion irradiated at 700 °C to simulate the high temperature irradiation environment of a fusion reactor interior after five years of active service. They then evaluated the material’s performance by characterizing the nanoscale defect distribution using transmission electron microscopy, revealing peak swelling in the W phase of approximately 0.03% and 0.68% in the γ-phase (Ni–Fe-W) under irradiation conditions. Additionally, a novel multi-projection high angle annular dark field (HAADF)  scanning TEM approach was used to determine the extent of damage segregation along the dual-phase W-to-γ interface. These interphase boundaries were found to possess an 11.8% areal coverage of defects along the boundary plane, which is anticipated to adversely affect overall material toughness. 

Contact

Jacob Haag  
Pacific Northwest National Laboratory   
Jacob.haag@pnnl.gov

Funding

This research was supported by the Department of Energy, Office of Science, Fusion Energy Sciences, Fusion Materials and Internal Components program under FWP13784, and was performed at the Pacific Northwest National Laboratory.