Anisotropic threshold stress intensity factor, KIH and crack growth rate in delayed hydride cracking of Zr-2.5Nb pressure tubes |
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Authors: | Young Suk Kim Sung Soo Kim Sang Chul Kwon Yong Moo Cheong Kyung Soo Im |
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Affiliation: | (1) the Korea Atomic Energy Institute, 305-353 Daejon, Korea |
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Abstract: | The objectives of this study are to systematically investigate the delayed hydride cracking (DHC) velocity and the threshold-stress
intensity factor, K
IH
, of a Zr-2.5Nb pressure tube as a function of orientation and elucidate the cause of this anistropic DHC behavior. The DHC
velocity as a function of orientation was determined using flattened cantilever beam specimens with 60 ppm H while the threshold-stress
intensity factor K
IH
, was evaluated as a function of orientation on the curved compact-tension (CT) and cantilever-beam (CB) specimens charged
with hydrogen to 200 ppm H. To infer a difference in a stress gradient ahead of the crack tip as a function of orientation,
tensile tests were conducted at temperatures ranging from room temperature (RT) to 560 °C using small tensile specimens of
2-mm-gage length taken from three directions of the tube. A textural change was investigated by comparing the inverse pole
figures before and after DHC while the {10
7} pole figures were constructed to find out the growth pattern of the DHC crack as a function of orientation. Faster DHC
velocity and lower K
IH
were obtained over temperatures of 170 °C to 270 °C, when the DHC crack grew in the longitudinal direction of the Zr-2.5Nb
pressure tube. The strain hardening after yielding and the extent of the textural change accompanied by DHC were higher in
the longitudinal direction of the tube, suggesting a higher stress gradient ahead of the crack tip. Thus, the anisotropic
DHC behavior of a Zr-2.5Nb pressure tube is discussed based on the stress gradient ahead of the crack tip governed by strain-hardening
rate after yielding and a change in texture accompanied by DHC, and the distribution of the {10
7} hydride habit planes.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. |
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Keywords: | |
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