Temperature Dependence of Fatigue Crack Propagation in Niobium-Hydrogen Alloys

Abstract

The effects of temperature on near-threshold fatigue crack growth rate have been investigated in niobium-hydrogen alloys. Fatigue tests were performed at 273 and 400 K on hydrogen-free specimens as well as on specimens containing hydrogen in solid solution and in the form of hydride. Compact tension specimens were tested using a tension-tension loading cycle at a frequency of 4 Hz and a load ratio of 0.05. At both temperatures, the results show that the threshold stress intensity range ΔKth decreases with the addition of hydrogen and reaches a minimum value at a critical hydrogen concentration. As the hydrogen concentration exceeds the critical concentration, ΔKth increases with the increase of the amount of dissolved hydrogen. The minimum threshold stress intensity range (ΔKth)min also increases linearly with the increase in temperature. Analysis of results suggests that the presence of hydrides cannot be responsible for the embrittle-ment of niobium with hydrogen, and that some more mobile form of hydrogen clusters is likely to cause the embrittlement.