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Title: Effect of hydrogen on the corrosion performance of zirconium alloys
Author: Wei, Jianfei
ISNI:       0000 0004 2719 348X
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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This study is part of the multidisciplinary research program funded by the EPSRC aimed at further understanding the mechanisms behind the oxidation, transition and breakaway of zirconium alloys. The current study concentrates on the effect of artificially introduced hydride rich rim region upon the corrosion performance of zirconium alloys. The methodology of cathodic hydrogen charging of zirconium specimen has been described. The intention is to create a hydride rich rim similar to observation made in end-of-life fuel claddings from nuclear reactor. The overall hydrogen levels in the samples were determined via inert gas fusion and the local hydride volume fractions via laboratory x-ray diffraction. The residual stress state in the rim was investigated by synchrotron x-ray diffraction. The rim was determined to have local hydrogen levels about 11,000 wt.ppm and predominantly δ-hydrides. Hydrided samples and their references were tested in autoclaves simulating primary water environment. Reference samples exhibited typical corrosion kinetics with a change from pre- to post-1st transition. The duration before 1st transition varies with alloy chemistry and heat treatment conditions. Hydrided samples generally experienced accelerated corrosion while the extent to which the material was affected depends on alloy chemistry. Parabolic rather than cubic oxide growth with a very slow early corrosion rate was recorded in hydrided alloys. Both hydrided and reference samples of three Zr-Sn-Nb alloys, ZIRLOTM, low tin ZIRLO and X2 with tin concentration ranging from 0.14 to 0.92 wt.% became the gravity of further characterisations since they exhibited improved corrosion performance with decreasing tin content. The microstructure of the oxide was investigated via cross-sectional Scanning Electron Microscope (SEM). The residual stress state in tetragonal and monoclinic phases as well as tetragonal phase fraction were studied via synchrotron x-ray diffraction, showing high in-plane compressive stresses in the oxide of different levels depending on the phase and alloy. The presence of a hydride rim lowered the residual stress. White oxide in hydrided samples displays lower residual stress level, smaller tetragonal phase fraction and higher degree of oxide grain misorientation when compared to black oxide regions of reference and hydrided samples. It was also found that the hydride rim region undergoes local depletion of hydrides in alloy with low Sn content during the early stage of aqueous corrosion. Finally a model was given to describe the different roles played by individual oxide and hydride phases during the oxidation of zirconium alloys.
Supervisor: Preuss, Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available