When 3:30 PM - 5:30 PM Dec 06, 2016
Where 1109 FXB Building
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Effects of Oxide Structure and Solute Distributions on the Stability of Zirconium Oxide Growth


Yan Dong
Thesis Defense

Waterside corrosion and associated hydrogen generation remain a major limiting factor for the use of zirconium alloys as cladding materials in the event of severe fuel duty conditions. Although it has been observed that corrosion behaviors strongly depend on minor alloying additions, the reasons for these differences remain unclear. This study focuses on the oxide structure and solute distribution near and within the oxide layers formed on different Zr alloys. Three alloys were selected and were corroded in 360°C water for 1 to 456 days. Zircaloy-4, a commercial alloy, shows a growth behavior with well-defined periodic transitions. Pure Zr loses protectiveness right away, while alloy Zr-Fe-Cr, created by adding small amount of Fe and Cr to Zr, show protective behavior for the whole duration of the test. The corroded alloys were analyzed through a multi- scaled characterization approach combining scanning electron microscopy, focused ion beam milling, transmission electron microscopy, and atom probe tomography. A consistent sequence of oxygen enriched phases is observed ahead of ZrO2 oxide front in all alloys. The sub-oxide phase exhibits different thicknesses and morphologies at different stage of oxidation and in different alloys. Solute distributions are modified as solutes are incorporated into oxide, exhibiting signs of rejection by oxide front or segregation at specific site within the oxide scale. The redistribution of solutes (clustering and segregation) at the metal/oxide interface, in the solid solution region adjacent to interface, and within the oxide, can change the structures and properties of the oxide phase and therefore affecting the oxidation kinetics. The synergy between oxide structure and chemistry is speculated to promote preferential oxide growth along the metal grain boundaries in pure Zr.

 

DISSERTATION COMMITTEE:

Chair: Assoc. Prof. Emmanuelle Marquis, MSE

Members Prof. Katsuyo Thornton, MSE

Prof. Lumin Wang, NERS

Cognate: Prof. Michael Atzmon, NERS