Comprehensive study on the mechanical properties of δ-zirconium hydride grown in a Zr2.5%Nb matrix

Abstract

Zirconium alloys are used in the nuclear industry because of low neutron capture cross-section, appropriate mechanical properties, and corrosion resistance. In-reactor, the zirconium components undergo hydrogen pick-up, mainly due to corrosion occurring along the component and with the steel end-fittings. When the hydrogen reaches a threshold terminal solid solubility, the precipitation of zirconium hydride occurs. This thesis investigates the mechanical properties of this hydride precipitate, under different conditions and using different techniques to assess those properties.

After the introductory Chapters (1 and 2), Chapter 3 includes details regarding the methodology used in subsequent chapters.

Chapter 4 presents the mechanical properties (at room (RT) and high temperatures (HT)) of the δ-zirconium hydride grown in two different structures (rim and blister) using a combination of nanoindentation and modelling. At RT, the measured hardness of the hydride rim was 3.73GPa, while the hydride blister was 3.5GPa. The RT yield strength values obtained via models were 904MPa and 890MPa using one model, and 869MPa and 862MPa with the second, for the rim and blister, respectively. The HT hardness decreased linearly with increasing temperature.

Chapter 5 shows a novel result of the impact of proton irradiation on the hardness of δ-zirconium hydride and Zr2.5%Nb. The true hardness of the δ-zirconium hydride increased from 3.0±0.12GPa at 0dpa, to 4.31±0.35GPa at 0.8dpa, while Zr2.5%Nb increased from 2.53±0.12GPa at 0dpa to 3.03±0.21GPa at 0.8dpa. The yield strength of the δ-zirconium hydride increased from 862MPa at 0dpa, to 1146MPa at 0.8dpa, and the Zr2.5%Nb increased from 662MPa at 0dpa to 850MPa at 0.8dpa. In addition, both materials showed evidence that, up to 0.8dpa, there is still no saturation of irradiation defects.

Chapter 6 investigates the mechanical properties, and the deformation mechanisms, of the δ-zirconium hydride via micropillar compression, and ex-situ TEM investigation. The hydride yield strength obtained from the stress-strain curves was 1084±125MPa. TEM investigation of the deformed micropillar showed the formation of dislocations inside the hydride, characterized as belonging to a typical FCC slip system.

Lastly, Chapter 7 gives a summary of the conclusions, correlations between each chapter, and future work recommendations.