Abstract
The effects of hydrogen on near-threshold fatigue crack growth rate have been investigated in niobium at room temperature. Fatigue tests were performed on a hydrogen-free specimen as well as specimens containing hydrogen in solid solution and in the form of hydride. Specimens were tested using a tension-tension loading cycle at a frequency of 4 Hz and two load ratios of 0.05 and 0.4. The results show that the threshold stress-intensity factor ΔKth decreases with the addition of hydrogen and reaches a minimum at a hydrogen concentration approximately equal to the solubility limit of hydrogen in niobium. As the hydrogen concentration exceeds the solubility limit, ΔKth increases with the increase of the amount of hydrogen dissolved in the specimen. Analysis of this behavior suggests that stress-induced hydride cannot be responsible for the embrittlement of niobium with hydrogen, and dislocation-hydrogen interaction plays an important role in the embrittlement process. SEM metallography studies also confirm the importance of dislocation in the embrittlement of niobium by hydrogen.
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