Abstract
As part of the MUZIC-2 project, several state-of-the-art high resolution analysis techniques
are being used to study the microstructure of a range of commercial and developmental Zr
alloys corroded under autoclave simulated PWR conditions. Samples were chosen to be
representative of the early, pre-transition, transition and post-transition stages of the
oxidation process. We have studied the development of the equiaxed-columnar-equiaxed
grain structure, and observe that the columnar grains are both longer and show a stronger
preferred texture in more corrosion-resistant alloys. Fresnel imaging revealed the existence
of both parallel interconnected pores and some vertically interconnected pores along the
columnar oxide grain boundaries, which become disconnected near the metal-oxide interface.
Analytical (Scanning) Transmission Electron Microscope ((S)TEM) has been used to study
two types of second phase particles (SPPs): β-Nb and Zr(Nb,Fe)2. The Zr(Nb,Fe)2 SPPs are
present at a lower number density and tend to become amorphous quickly once incorporated
into the growing oxide. Atom Probe Tomography (APT) was used to study finer Nb and Fe
clusters in the suboxide and metal regions, Fe clusters are also found at the oxide grain
boundaries. Electron Energy Loss Spectroscopy analysis (EELS) and automated crystal
orientation mapping with TEM have also revealed Widmanstatten-type suboxide layers in
some samples with compositions in different regions of either the hexagonal ZrO structure
predicted with ab initio modelling or Zr3O2. Some of these layers are much thicker than
observed previously in other oxidised zirconium alloys. Hydrogen pickup mechanisms have
been studied by high resolution Secondary Ion Mass Spectrometry (NanoSIMS) analysis of
deuterium-spiked samples, showing that at different stages of oxidation the penetration of
deuterium occurs in quite different patterns. These observations are discussed in the context
of current models for oxidation and hydrogen pickup in zirconium alloys.
are being used to study the microstructure of a range of commercial and developmental Zr
alloys corroded under autoclave simulated PWR conditions. Samples were chosen to be
representative of the early, pre-transition, transition and post-transition stages of the
oxidation process. We have studied the development of the equiaxed-columnar-equiaxed
grain structure, and observe that the columnar grains are both longer and show a stronger
preferred texture in more corrosion-resistant alloys. Fresnel imaging revealed the existence
of both parallel interconnected pores and some vertically interconnected pores along the
columnar oxide grain boundaries, which become disconnected near the metal-oxide interface.
Analytical (Scanning) Transmission Electron Microscope ((S)TEM) has been used to study
two types of second phase particles (SPPs): β-Nb and Zr(Nb,Fe)2. The Zr(Nb,Fe)2 SPPs are
present at a lower number density and tend to become amorphous quickly once incorporated
into the growing oxide. Atom Probe Tomography (APT) was used to study finer Nb and Fe
clusters in the suboxide and metal regions, Fe clusters are also found at the oxide grain
boundaries. Electron Energy Loss Spectroscopy analysis (EELS) and automated crystal
orientation mapping with TEM have also revealed Widmanstatten-type suboxide layers in
some samples with compositions in different regions of either the hexagonal ZrO structure
predicted with ab initio modelling or Zr3O2. Some of these layers are much thicker than
observed previously in other oxidised zirconium alloys. Hydrogen pickup mechanisms have
been studied by high resolution Secondary Ion Mass Spectrometry (NanoSIMS) analysis of
deuterium-spiked samples, showing that at different stages of oxidation the penetration of
deuterium occurs in quite different patterns. These observations are discussed in the context
of current models for oxidation and hydrogen pickup in zirconium alloys.
| Original language | English |
|---|---|
| Title of host publication | Proceedings of the TopFuel conference 2015 |
| Publication status | Published - 1 Sept 2015 |