Influence of Cr addition on microstructure of a 5% Re-containing single crystal nickel-based superalloy

Based on a 5% (mass fraction) Re-containing single crystal nickel-based superalloy with 3% (mass fraction) Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ′ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ′ lattice misfit becomes more negative. According to the energy dispersive spectroscopy (EDS) results, Cr is mainly distributed in the γ matrix; and more γ-forming elements, such as Re and W, enter the γ matrix, while the γ/γ′ partition ratio of Cr is inversely decreased.