Fatigue crack growth behavior in niobium-hydrogen alloys |
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| Authors: | Mark Ching-Cheng Lin K. Salama |
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| Affiliation: | (1) Present address: Department of Mechanical Engineering, University of Houston, Hsinchu City, Taiwan, Republic of China;(2) Materials Research Laboratoires, Industrial Technology Research Institute, Hsinchu City, Taiwan, Republic of China;(3) The Department of Mechanical Engineering, University of Houston, 77204-4792 Houston, TX |
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| Abstract: | Near-threshold fatigue crack growth behavior has been investigated in niobium-hydrogen alloys. Compact tension specimens (CTS) with three hydrogen conditions are used: hydrogen-free, hydrogen in solid solution, and hydride alloy. The specimens are fatigued at a temperature of 296 K and load ratios of 0.05, 0.4, and 0.75. The results at load ratios of 0.05 and 0.4 show that the threshold stress intensity range (ΔK th ) decreases as hydrogen is added to niobium. It reaches a minimum at the critical hydrogen concentration (C cr ), where maximum embrittlement occurs. The critical hydrogen concentration is approximately equal to the solubility limit of hydrogen in niobium. As the hydrogen concentration exceeds C cr , ΔK th increases slowly as more hydrogen is added to the specimen. At load ratio 0.75, ΔK th decreases continuously as the hydrogen concentration is increased. The results provide evidence that two mechanisms are responsible for fatigue crack growth behavior in niobium-hydrogen alloys. First, embrittlement is retarded by hydride transformation-induced and plasticity-induced crack closures. Second, embrittlement is enhanced by the presence of hydrogen and hydride. |
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