Phase transformations during cooling from the βZr phase temperature domain in several hydrogen-enriched zirconium alloys studied by in situ and ex situ neutron diffraction

Abstract

In hypothetical accidental conditions, zirconium-based nuclear fuel claddings can absorb high hydrogen contents (up to several thousand wppm) and be exposed to high temperatures (β Zr phase temperature range) before being cooled. This paper thoroughly investigates the microstructural and microchemical evolutions that take place in such

Combined effects of temperature and of high hydrogen and oxygen contents on the mechanical behavior of a zirconium alloy upon cooling from the βZr phase temperature range

“…Besides, it could be due to the microstructure of the prior-βZr materials tested in this study as a result of the cooling rate applied [41]. However, despite these deviations, the trends are fully consistent.…”

“…The hardening effect of hydrogen in this temperature range would be related to the contribution of zirconium hydrides that extensively precipitate via a eutectoid transition taking place at around 500-550°C [41]. Besides, it may result from a significant amount of hydrogen potentially remaining in solid solution within the Zr matrix, as reported in [41]. However, the hydrogen-related effect appears not to significantly depend on the oxygen content.…”

“…Additionally, for a given oxygen content and at a given temperature below 500°C, the YS and UTS increase considerably in the presence of hydrogen up to 3000 wppm. The hardening effect of hydrogen in this temperature range would be related to the contribution of zirconium hydrides that extensively precipitate via a eutectoid transition taking place at around 500-550°C [41]. Besides, it may result from a significant amount of hydrogen potentially remaining in solid solution within the Zr matrix, as reported in [41].…”

“…This additional oxygen is likely to have a significant effect on the embrittlement of the material. Besides, the faster cooling rate applied by Brachet et al [13] probably induces additional embrittlement caused by the hardening effects of finer microstructure constituted by a significant amount of hydrogen remaining in solid solution within the Zr matrix and submicrometric hydrides, as observed in [41]. Furthermore, according to Bai [38], the materials tested at a faster strain rate exhibit lower ductility for a given set of hydrogen content and testing temperature, potentially resulting from the material viscosity.…”

“…However, it can be mentioned that this failure mode mixing brittle and ductile fracture at the microscale is mainly related to microchemical heterogeneities (oxygen and hydrogen in particular) due to partitioning during the βZr-to-αZr phase transformation upon cooling [24]. The distribution of oxygen and hydrogen, the fraction of hydrogen precipitated in the form of hydrides (or remaining in solid solution in the Zr matrix), the nature of hydrides and their proportion strongly depend on the cooling scenario and the average oxygen and hydrogen contents [26,41].…”