Hydrogen redistribution during hydride precipitation in Zr-2.5Nb pressure tubes

Hydrided furnace-cooled and water-quenched samples of Zr-2.5Nb pressure tube were studied in order to aid comprehension as regards the hydrogen redistribution that occurs during hydride precipitation in this material. Results showed a high fraction of gamma-hydrides grown at hoop-grains in the quenched condition, resulting from the strong reduction in diffusion times imposed by quenching. This also lead to variations in delta-hydride distribution, delta-hydride populations and hydrogen solubility (TSS) during subsequent thermal cycling, for which an interpretation based on the memory effect of hydride precipitation was proposed. Experimental observations suggest that hydrogen redistribution during cool-down from high temperature is controlled not only by certain preferential grains, but also by the presence of misfit dislocations left by pre-existing hydride particles. A hypothesis was presented to explain the differences in precipitation solubility (TSSP) between furnace-cooled and water-quenched material, which was associated to the possible influence of misfit dislocations on the driving force for hydrogen diffusion. (C) 2020 Elsevier B.V. All rights reserved.