Raman mapping of sectioned zirconium cladding oxides was performed to analyze different spectral features before and after breakaway, as well as between zirconium and its alloys Zr-2.65Nb, Zry-3, and Zry-4. Oxide phase composition, or percent tetragonality, was defined to compare tetragonal to monoclinic zirconia. Percent tetragonality was spatially mapped to support distinction of zirconia phase distribution. A tetragonal-rich layer was seen at the metal/oxide interface, while post-breakaway samples exhibited increased amount of tetragonal phase in the bulk of their oxides. Spatial mapping of spectral peak location and half-width at half-maximum was accomplished to distinguish differences in stability mechanisms of tetragonal-rich zirconia phase. Shifts in monoclinic peak positions provided mapping of relative stress state, supporting the differences in stabilization of tetragonal phase near the metal/oxide interface and tetragonal phase in the bulk of the oxide. Tetragonal phase near the metal/oxide interface is stabilized through support of oxygen sub-stoichiometry and compressive stress. Tetragonal phase observed in the bulk of the oxide is stabilized through oxygen sub-stoichiometry, void of compressive stress. A linear trend between percent tetragonality and stress state was determined. This resulted in a connection between mechanism of tetragonal to monoclinic phase transformation and a cladding's ability to resist oxidation and breakaway. Poor performing samples displayed greater stress gradients, driven by lattice mismatch at the metal/oxide interface, as well as between tetragonal and monoclinic phase boundaries. Tetragonal phase at the metal/oxide interface for superior performing samples have reduced epitaxial growth of tetragonal grains, lowering compressive stress gradients and provided more resistant inner-oxide layers. With increased utility of Raman spectroscopy for characterizing zirconium cladding materials, different degradation mechanisms can be further understood.
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Efaw, Corey M.; Vandegrift, Jordan L.; Reynolds, Michael; McMurdie, Samuel; Jaques, Brian J.; Xiong, Hui;...and Hurley, Michael F. (2019). "Characterization of Zirconium Oxides Part I: Raman Mapping and Spectral Feature Analysis". Nuclear Materials and Energy, 2, 1100707-1 - 100707-11. https://dx.doi.org/10.1016/j.nme.2019.100707