Zr alloys exhibit irradiation-induced growth and hardening which is associated with the defects and dislocation loops that form during irradiation. In this study, state-of-the-art in-situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM) techniques were used to investigate the stability of dislocation loops in two proton-irradiated Zr-Fe binary alloys in real time. Complementary data from both techniques show rapid annealing of a-loops occurs between 300°C and 450°C. Line profile analysis was performed on the SXRD patterns using the convoluted multiple whole profile analysis tool, to calculate the change in a-loop line density as a function of post-irradiation heat treatment temperature and time. At temperatures below 300°C, no significant decrease in a-loop density was detected when held for one hour at temperature. From this SXRD experiment, we calculate the effective activation energy for the annealing process as 0.46 eV. On-axis in-situ STEM imaging was used to directly observe a-loop mobility during heating cycles and confirm that a-loops begin to glide in the trace of the basal plane at ~200°C in a thin foil specimen. Such a-loop gliding events, leading to annihilation at the foil's surfaces, became more frequent between 300-450°C.

No abstract

No abstract

Automated crystal orientation mapping in the transmission electron microscope has been used to simultaneously map the phase, orientation and grain morphology of oxides formed on Zircaloy-2 after 3 and 6 cycles in a BWR reactor in unprecedented detail. For comparison, a region of a pre-oxidised autoclave-formed oxide was also proton irradiated at the Dalton Cumbrian Facility. The proton irradiation was observed to cause additional stabilisation of the tetragonal phase, attributed to the stabilising effect of irradiation-induced defects in the oxide. In the reactor-formed oxides, no extra stabilisation of the tetragonal grains was observed under neutron irradiation, as indicated by the similar tetragonal phase fraction and transformation twin boundary distributions between the non-irradiated and reactor-formed oxides. It is suggested that the damage rate is too low in the newly formed oxide to cause significant stabilisation of the tetragonal phase. This technique also reveals the oxide formed under reactor conditions has a more heterogeneous microstructure and the growth of well-oriented columnar monoclinic grains is significantly reduced when compared to a non-irradiated oxide. High angle annular dark field scanning transmission electron microscopy (HAADF STEM) also revealed the development of extensive networks of intergranular porosity and eventually grain decohesion in the

Understanding corrosion mechanisms is of importance for reducing the global cost of corrosion. While the properties of engineering components are considered at a macroscopic scale, corrosion occurs at micro or nano scale and is influenced by local microstructural variations inherent to engineering alloys. However, studying such complex microstructures that involve multiple length scales requires a multitude of advanced experimental procedures. Here, we present a method using correlated electron microscopy techniques over a range of length scales, combined with crystallographic modelling, to provide understanding of the competing mechanisms that control the waterside corrosion of zirconium alloys. We present evidence for a competition between epitaxial strain and growth stress, which depends on the orientation of the substrate leading to local variations in oxide microstructure and thus protectiveness. This leads to the possibility of tailoring substrate crystallographic textures to promote stress driven, well-oriented protective oxides, and so to improving corrosion performance.