FCC-Zr phase transformation-induced defect substructure in Zr2Si precipitates equilibrated in Si-modified Zircaloy-4

This work investigates the atomic scale substructure of interfaces in Zr2Si secondary phase precipitates formed by the stresses associated with the α-Zr (HCP) to γ-Zr (FCC) phase transformation and thermal effects in an experimental Si-modified Zircaloy-4 by means of transmission electron microscopy and CSL/DSCL (coincident site lattice/displacement shift complete lattice) models. Analysis of a high-angle twin interface reveals their characteristic principal primary Δg vectors, a typical feature of the singular interfaces, and the sessile twinning disconnections. The step height and length of the interfacial dislocation line, with the Burgers vector parallel to the habit plane, are analysed using the DSCL model. In the second case, a low-angle interface of mixed tilt-twist character is studied and facets of constant length along the densest-packed planes and ledges of inconstant height, a common feature of vicinal interfaces, are identified.