Growth of ZrO2 Corrosion Film on Zr-2.5%Nb Pressure Tube Alloy

Abstract

Abstract The microstructure of Zr-2.5wt%Nb pressure tubes used in CANDU reactors consists α-Zr grains with a [110] texture in the radial direction and surrounded by a thin layer of metastable β-Zr. Information on oxide formed on β-regions have been reported. For the predominantly monoclinic ZrO2 (a=0.514, b=0.521, c=0.531nm, β=99.2°) formed α-Zr, two types of grain morphology and texture have been observed. In some areas of the oxide, columnar grains with a fibre texture exhibit no specific orientation relationship with the metal; such regions are not the subject here. Results presented here address a textured growth mode which is sensitive to the metal orientation. Plan-view foils of oxide on the pressure tube radial-normal surface formed by a treatment of 24 hours in steam were prepared by ion-beam thinning and examined in a JEOL 2010 TEM. Selected area diffraction (SAD) and convergent beam diffraction (CBD) patterns showed that oxide growth mode was dominated by a [001] growth and consisted of a combination of orientation related [001] growth and mixed [001]/[100] growth.