The role of ?-Zr in a Zr-2.5Nb alloy during aqueous corrosion: A multi-technique study

The Zr–2.5Nb alloy is used as pressure tubes in Canadian Deuterium Uranium (CANDU) nuclear reactors, and the typical starting microstructure consists of ?-Zr grains elongated both transverse longitudinal directions thin layers partially decomposed ?-Zr lying between grains. In this study, we have state-of-the-art microscopy techniques to characterise long-term thermally ? phase alloy, oxide scale formed on them a reactor coolant loop with aim understanding mechanisms underpinning thermal decomposition behaviour at service temperatures exploring role controlling microchemistry zirconium oxide, hence its influence general corrosion resistance alloy. We observe that these are heavily even after short stress stage 400 °C end manufacturing cycle, closely packed array ?-Nb precipitates forming an matrix. shown oxidation bands significantly slower than surrounding matrix re-nucleated under each band. conclude it combination Nb-rich remnants original arising from hot extrusion drawing stages new dense offers significant barrier front (and also penetration hydrogenic species), so characteristic layered process very important determining overall behaviour.