Abstract
Hydrogen embrittlement (HE) of niobium was investigated in 1.1 MPa hydrogen and helium from room temperature to 80 K with the strain rates of 4.2×10−2∼4.2×10−5 s−1 by using the specially designed equipment. HE increased with decreasing temperature, reached a maximum, and then decreased rapidly with decreasing temperature. The maximum HE temperature decreased with decreasing strain rate, namely HE increased with increasing strain rate above 200 K while that increased with decreasing strain rate below 200 K in result. Cleavage fracture was mainly observed in hydrogen, while ductile rupture was observed in helium. Dimple rupture was also observed in hydrogen below 100 K. It is discussed that HE is caused by hydride formation at the crack tip, where HE above 200 K is controlled by the fracture of the hydride and that below 200 K is controlled by hydrogen diffusion to form the hydride.
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