Kinetics of zirconium hydride precipitation and reorientation studied using synchrotron radiation
Open Access
- Author:
- Colas, Kimberly Barbara
- Graduate Program:
- Nuclear Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Arthur Thompson Motta, Thesis Advisor/Co-Advisor
Arthur Thompson Motta, Thesis Advisor/Co-Advisor - Keywords:
- precipitation kinetics
synchrotron radiation
zirconium hydrides - Abstract:
- Hydrogen ingress into zirconium alloy fuel cladding during corrosion can degrade cladding performance as a result of the formation of brittle hydrides. Hydride platelets normally precipitate with the platelet habit plane in the transverse-rolling plane of the sheet and are homogeneously distributed through the cladding thickness. Once hydrogen enters the cladding it can respond to a combination of temperature and stress such that hydrides particles reorient with their habit planes normal to the sheet surface and processes such as delayed hydride cracking may occur by preferential reoriented hydride precipitation at crack tips. This reorientation of hydrides can severely reduce ductility, thus it is crucial to understand the kinetics of hydride dissolution and precipitation under stress at temperature. Studies of hydrogen behavior in zirconium alloys are normally performed post facto, and suffer both from a scarcity of data and from the confounding effects of studying a hydride microstructure different from that present at higher temperature. In the current study we have used synchrotron radiation diffraction to study the kinetics of hydride precipitation and dissolution in situ (under stress and at temperature). Samples of Zircaloy-4 and Zircaloy-2 hydrided between 80 and 610 wt.ppm and cut in different orientations were examined by transmission x-ray diffraction (using 80 keV synchrotron radiation), while heated and cooled in a furnace at temperatures ranging from 20 to 550ºC and stresses up to 100 MPa. Under these conditions the hydrides dissolved and re-precipitated in a different orientation under sufficiently high stress. A careful study of the intensities and peak broadening of the diffraction peaks as a function of time, stress and temperature allowed the identification of specific characteristics of the diffraction patterns of reoriented hydrides. As a result, the kinetics of dissolution, re-precipitation and orientation of the hydrides could be followed continuously by monitoring the peak broadening of diffraction peaks. The analysis of the diffraction patterns allowed detailed understanding of the kinetics of the hydride evolution under temperature and stress. Additional experimental techniques were used to enhance the understanding of hydrides in the material such as metallography and reflection x-ray diffraction using synchrotron radiation. Finally a preliminary experiment was performed using micro-beam synchrotron radiation to study hydride precipitation at a crack tip while under stress. The experiment was done at room temperature and under no load on a hydrided cracked sample, and showed the viability of using micro-beam synchrotron radiation to study hydride precipitation at a crack tip.