Bulk Hydrides and Delayed Hydride Cracking in Zirconium Alloys
MetadataShow full item record
Zirconium alloys are susceptible to engineering problems associated with the uptake of hydrogen throughout their design lifetime in nuclear reactors. Understanding of hydrogen embrittlement associated with the precipitation of brittle hydride phases and a sub-critical crack growth mechanism known as Delayed Hydride Cracking (DHC) is required to provide the engineering justifications for safe reactor operation. The nature of bulk zirconium hydrides at low concentrations (< 100 wt. ppm) is subject to several contradictory descriptions in the literature associated with the stability and metastability of γ-phase zirconium hydride. Due to the differing volume expansions (12-17%) and crystallography between γ and δ hydride phases, it is suggested that the matrix yield strength may have an effect on the phase stability. The present work indicated that although yield strength can shift the phase stability, other factors such as microstructure and phase distribution can be as or more important. This suggests that small material differences are the reason for the literature discrepancies. DHC is characterised by the repeated precipitation, growth, fracture of brittle hydride phases and subsequent crack arrest in the ductile metal. DHC growth is associated primarily the ability of hydrogen to diffuse under a stress induced chemical potential towards a stress raiser. Knowledge of the factors controlling DHC are paramount in being able to appropriately describe DHC for engineering purposes. Most studies characterise DHC upon cooling to the test temperature. DHC upon heating has not been extensively studied and the mechanism by which it occurs is somewhat controversial in the literature. This work shows that previous thermo-mechanical processing of hydrided zirconium can have a significant effect on the dissolution behaviour of the bulk hydride upon heating. DHC tests with γ-quenched, furnace cooled-δ and reoriented bulk hydrides upon heating and DHC upon cooling suggest that the amount of hydrogen in solution is the primary factor controlling the occurrence of DHC and consistent with the postulation that the stress induced chemical potential is the driving force for DHC.
URI for this recordhttp://hdl.handle.net/1974/6969
Request an alternative formatIf you require this document in an alternate, accessible format, please contact the Queen's Adaptive Technology Centre
Showing items related by title, author, creator and subject.
Fang, Qiang (2016-03-01)This thesis tries to fill some of the missing gaps in the study of zirconium hydrides with state-of-art experiments, cutting edge tomographical technique, and a novel numerical algorithm. A new hydriding procedure is ...
Phase transformation and microstructural changes during the hydriding and aging processes in dual phase Zr alloy Shiman, Oksana V.; Daymond, Mark R. (Elsevier BV, 2019-06-01)The Zr-2.5 wt%Nb alloy was studied in order to elucidate phase transformations and the distribution/redistribution of hydrogen. The study focuses on understanding the stability of the ZrH system; surface hydride formation ...
The development and characterization of a nickel/metal hydride microbattery for microfluidic applications Falahati, Hamid (2015-07-23)Micro Electro Mechanical Systems as well as Microfluidics are versatile technologies which have been evolved due to the advantage of miniaturization over the last decades. However, the majority of microfluidic devices are ...