Atom probe study of second-phase particles in Zircaloy-4

• Two types of second phase particles (SPPs) in Zircaloy-4 (Zy-4) were detected by atom probe tomography, Zr(Fe,Cr)2 and Zr2(Fe,Si). • DFT modelling determines the site preference of Si in Zr2(Fe,Si). • Impurity Cu and B atoms also segregate to the interfaces between the precipitates and the matrix. Zirconium (Zr) alloys, such as Zircaloy-4 (Zy-4), are widely used for cladding in nuclear applications. Zy-4 consists of an α-Zr matrix and various second phase particles (SPPs). These precipitates play a crucial role in determining the overall alloy performance, so understanding their composition is essential for the development of these nuclear materials. We have studied two SPPs in this alloy, Zr(Fe,Cr) 2 and Zr 2 (Si,Fe), using site-specific focused ion-beam lift-out and atom probe tomography, and measured the composition and distribution of alloying elements at the precipitate/matrix interface. Residual Cu and B segregated to the interfaces of both precipitates and the matrix while Sn only segregated to the interface in the Zr 2 (Fe,Si) precipitate. Hydrogen segregation was observed at the interface of Zr(Fe,Cr) 2 and the matrix.