Small-angle X-ray scattering study of Zr 4(Fe,Cr) precipitate in beta-quenched zircaloy-4

Abstract

Zircaloy-4 through beta quenching treatment has been extensively used as cladding and core structure material in water-cooled nuclear reactors, due to its high nodular corrosion resistance and mechanical strength. Research shows that corrosion resistance is highly related to the sites and size distribution of the second phase precipitate particles after quenching. The nodular corrosion resistance decreases as particle size increases, while uniform corrosion resistance increases. The existence of a large amount of quenched-in vacancies enhances the nucleation and growth of precipitates during the quench process. The microstructure of zircaloy-4 transforms from beta phase (bcc) to Widmanstaetten alpha phase (hcp) with a lathe structure by martensitic transformation. The main intermetallic precipitates, Zr{sub 4}(Fe,Cr), with a fcc phase mostly precipitated at the lathe boundaries, having sizes from 4 to 35 nm. These particles can be considered as a polydispersive system. SAXS (Small-Angle X-ray Scattering) technique, which is used in this study, is a powerful tool to determine the size distribution of fine particles. The IFT (Indirect Fourier Transformation) method is used in this study to analyze the measured scattering intensity distribution which comes from the scattering of all particles (below 50 nm) within the specimen. This work attempts to more accurately reconstructmore » or determine the size distribution of the second phase particles in beta-quenched zircaloy-4 without prior assumption of the shape of size distribution. The results can be used in future work to explore the mechanism of growth kinetics of Zr{sub 4}(Fe,Cr) precipitate.« less