Evaluation of Nb-base alloys for the divertor structure in fusion reactors

Niobium-base alloys are candidate materials for the divertor structure in fusion reactors. For this application, an alloy should exhibit resistance to aqueous corrosion, hydrogen embrittlement, and radiation damage and should have high thermal conductivity and low thermal expansion. Results of corrosion and embrittlement screening tests of several binary and ternary Nb alloys in high-temperature water indicated that Nb-1Zr, Nb-5Mo-1Zr and Nb-5V-1Zr (wt.%) showed sufficient promise for further investigation. These alloys, together with pure Nb and Zircaloy-4, have been exposed to high-purity water containing a low concentration of dissolved oxygen (<12 ppb) at 170, 230, and 300°C for up to ≈3200 h. Weight-change data, microstructural observations, and qualitative mechanical-property evaluations reveal that Nb-5V-1Zr is the most promising alloy at higher temperatures. Below ≈200°C, the alloys exhibit similar corrosion behavior