Corrosion fatigue of refractory materials with corrosion resistance to boiling nitric acid

Motooka, Takafumi; Kiuchi, Kiyoshi

Refractory metals such as Zr, Nb and Ti alloys with the excellent corrosion resistance in boiling nitric acid have been selected for structural materials of spent fuel reprocessing equipment. On this study, the fatigue crack growth rate of these materials was investigated by load control tests as a function of the stress intensity in boiling nitric acid and in air at room temperature. The fracture surface was observed by scanning electron microscopy. The crack growth rate of Zr and Nb was enhanced in boiling nitric acid compared with that in air at room temperature. Acceleration effect due to corrosion fatigue was not observed in the crack growth of Ti-5Ta alloy. The fracture surfaces of Ti-5Ta alloy showed the ductile striation in both environments. On the other hand, the fracture surfaces of Nb showed the ductile striation in air and brittle striation in nitric acid. The anodic dissolution was interpreted to the acceleration factor on corrosion fatigue of Nb. The fracture surfaces of Zr in nitric acid showed both brittle and ductile fracture with fluted pattern due to SCC.