M.A.Sc. Candidate
Dep. of Mechanical and Materials Engineering,
Nicol Hall, 60 Union Street, Kingston, K7L 3N6, Ontario, Canada
Tel: (613) 533 6000 Ext: 77594
Email: 4et11[at]queensu[dot]ca
Biography
B.Sc.Eng: Mechanical Engineering (Materials Option)
Queen’s University, September 2005 to April 2009
Current Research Fields
- Delayed Hydride Cracking
- Hydride Phase Quantification
- γ/δ Zirconium Hydride Phase Transformations
Research Interests
Hydrogen ingress into zirconium alloys can result in the formation of brittle hydride precipitates. These brittle hydrides can result in the degradation in the mechanical properties of the material as well as enable a failure mechanism known as Delayed Hydride Cracking (DHC). Hydrides at low hydrogen concentrations (~100ppm) are known to form two distinct hydride phases: fcc δ-hydride and ‘metastable’ fct γ-hydride. Fundamental understanding of both the conditions of formation and effects of each phase on material behaviour is important for the development of correct engineering models for use in the nuclear industry.
There have been many studies with considerable disagreement regarding both the formation conditions and phase stability of the two zirconium hydride phases. The conventional understanding is that γ-hydride is a metastable phase which only forms upon quick quenches from the solubility limit and will transform into stable δ-hydride upon ageing treatments. However, studies in the literature have shown both a δ→γ phase transformation as well as a confirmation of γ-hydride stability. This suggests either experimental error or the ability of the hydride phase stability can be shifted by thermo-mechanical processing. A recent study used synchrotron x-ray diffraction at NSLS to measure the changes in hydride populations resulting from altering the materials yield strength and quench rate. Ultimately it was determined that although the yield strength did significantly affect the hydrogen populations, hydride phase formation and stability is more complicated. Some of the results suggest that the ability of the hydrogen to diffuse in the material plays a strong role in this behaviour. However, this does indicate that the discrepancies in the literature may be a result of minute material differences. Fig. 1 shows a representation of the hydrogen population as a result of quench rate and material.
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| Fig. 1. Hydride populations produced in various zirconium alloys upon different soultionizing/quenching treatments |
Currently studies on the effects of hydride phase and orientation on DHC crack behaviour are underway. Tests to determine the differences in KIH and cracking velocities for Zr-2.5 wt% Nb pressure tube materials with γ, δ (natural orientation) and δ (reoriented) hydride populations are to be completed. This will provide additional insight into the mechanism of operation for DHC.