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Effect of proton irradiation and hydriding on strain localisation in zirconium alloys

Thomas, Rhys

[Thesis]. Manchester, UK: The University of Manchester; 2020.

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Abstract

Zirconium alloys are utilised by the nuclear industry as a structural and clad material for use in power reactors. The integrity of these components is crucial for efficient and safe generation of power. During operation, neutron irradiation and hydride formation due to corrosion impact yield stress and ductility. The aim of the present PhD project was to characterise the change in deformation behaviour of zirconium alloys exposed to irradiation and hydrides using a combination of high resolution digital image correlation and electron backscatter diffraction techniques. In order to generate accurate displacement maps using digital image correlation, a pattern at a suitable length scale must be generated on the surface of the sample. The styrene vapour assisted gold remodelling technique was chosen to produce a speckle pattern. The remodelling temperature and time were optimised and strain maps of non-irradiated ZIRLO were created to ensure suitability for investigating sub-grain scale deformation. Proton irradiation was performed as a surrogate for the neutron flux encountered in-reactor and strain localisation was studied in Zircaloy-4 samples irradiated to 0.1 dpa. Dramatically enhanced strain localisation was observed as a result of irradiation and was attributed to the creation of defect-free channels. Due to the texture in zirconium alloys, deformation along different principal directions was performed and slip system activation was quantitatively measured for both non-irradiated and irradiated conditions. Differing slip system activation was observed for loading along the rolling direction compared loading along the transverse direction, however no significant change in slip system activation was observed due to irradiation. Finally, strain localisation in a sample containing hydrides induced by cathodic charging and homogenisation heat treatment was investigated. The average amount of strain observed within hydrides and second phase particles was lower than that in the matrix and shear bands were observed to terminate at transgranular hydrides. As well as providing an improved understanding of the impact of irradiation and hydrides on strain localisation in zirconium alloys, the methods developed will allow further investigation of deformation behaviour in corrosion-susceptible materials. Quantitative displacement maps and slip system activation data will allow for validation of crystal plasticity models, used to predict deformation behaviour of components subject to in-reactor degradation.