Nanoscale Characterization of the Metal-Oxide Interface on a Zr-2.5Nb Alloy (50)

Abstract

Canada Deuterium Uranium (CANDU) reactors use Zr–2.5Nb alloy for pressure tubes, and the typical starting microstructure consists of elongated α+β grains. In this study, the microstructure near the metal-oxide interface of a Zr-2.5Nb alloy is characterized after 567 days of exposure to high temperature water. Fresnel imaging was carried out using transmission electron microscopy to investigate the type, distribution, and connectivity of nano-porosity through the oxide layer. The observed nano-porosity may provide shot-circuit pathways for the transport of hydrogen or ions through the film to the metal/oxide or oxide/solution interfaces. Scanning transmission electron microscopy (STEM) is used to study the microstructure of the oxide and energy-dispersive X-ray (EDX) spectroscopy is used to reveal the element distributions. A key observation was decomposition the of β phase at the metal-oxide interface.