Difference in corrosion fatigue behavior between Ti-5Ta alloy and zirconium in boiling nitric acid

Motooka, Takafumi; Kiuchi, Kiyoshi

Ti-5Ta alloy and zirconium with excellent corrosion resistance to nitric acid have been used as equipment materials in spent fuel reprocessing plants. However, zirconium has the susceptibility to stress corrosion cracking in nitric acid solutions. The fatigue crack growth rates of both metals were examined to clarify the effect of stress corrosion cracking on the fatigue crack growth in boiling 17% nitric acid. The fatigue crack growth behavior of Ti-5Ta alloy in nitric acid showed almost the same behavior as seen in air. The crack growth rate is slightly enhanced in nitric acid. The fracture surface showed the ductile striation with independence on the loading direction. On the other hand, the fatigue crack growth rate of zirconium is remarkably accelerated in nitric acid. The fatigue crack growth was affected by the cracking mode composed of the pseudo-cleavage and plastic deformation. The difference in fatigue cracking behavior on both metals in nitric acid is interpreted with the difference in a cross slip system and the corrosion resistance in nitric acid.