Study of optimum composition of extra high purity Nb-W alloy for reprocessing condition with boiling nitric acid

Ioka, Ikuo  ; Suzuki, Jun; Kiuchi, Kiyoshi; Nakayama, Jumpei*

An Extra high purity Nb-W alloy (Nb-W EHP) that is superior to current Zr for cracking in severer environment is developed for reprocessing plants. Nb-W EHP has a technical limitation in weldability for practical use. To choose an optimum composition range of W, Nb-W EHP with different content of W were manufactured. Weld joint specimens were prepared by TIG welding. Tensile, corrosion and Charpy impact tests were carried out to examine the effect of W on chemical and mechanical properties of Nb-W EHP. There was little effect of W on corrosion rate of weld joint of Nb-W EHP. The increase in W improves ultimate tensile strength of Nb-W EHP. A ductile-brittle transition temperature (DBTT) of Nb-W EHP increased with an increase in W. The increase in DBTT is a problem as a structural material. Moreover, DBTT of the weld joint was high about 150K in comparison with the base metal. It is necessary to adjust W content to 8wt% or less in Nb-W EHP from the obtained results.