Characterization of topologically close-packed phases and precipitation behavior of P phase in a Ni-based single crystal superalloy

Scanning electron microscopes (SEM) and transmission electron microscopes (TEM) were employed to investigate the topologically close-packed (TCP) phases in an experimental nickel base single crystal superalloy. Orientation relationships between P phase and matrix were found as (010)_P//(11‾1)_γ and [201]_P//[110]_γ, in which atomic arrangement of P phase obtains the optimal matching with that of γ/γ’ matrix and the semi-coherent interface forms, achieving the lower interface energy. The elemental composition, atomic arrangement of low index planes and the atomic attachment of P phase with matrix were analyzed in detail to investigate the atomic scale structure of the fast-growing semi-coherent interface and its effects on precipitate growth. Finally, the nucleation of P phase was discussed.