Formation mechanism of composite secondary phase particles in a solution-treated Si-modified Zircaloy-4

Zr-Si binary precipitates affect mechanical and corrosion properties of Si-modified Zircaloy-4. In this study, composite secondary phase precipitates, having a core of C16 Zr2Si precipitate semi-coated with C15 Zr(Fe,Cr)2 Laves phase, were analysed as observed after solution treatment of experimental Si-modified Zircaloy-4. Crys-tallographic orientation relationship between the body-centred tetragonal (BCT) Zr2Si and face-centred cubic (FCC) Zr(Fe,Cr)2 Laves phase regions was determined to be (101)C16 // (110)C15 and [111]C16 // [111]C15. Two regions formed an incoherent interface accommodating about 30 % misfit strain, calculated by Bramfitt two-dimensional lattice mismatch criterion. The mechanism of formation of composite precipitates was described which, in turn, outlines the way for manipulating microstructure of composite precipitates to further optimise mechanical properties of Si-modified Zircaloy-4.