The solidification characteristics of high refractory content nickel based superalloy single crystals have been studied over a wide range of composition. To assess the influence of composition on distribution coefficients, quantitative segregation mapping experiments have been conducted on as cast single crystals. Additionally, differential thermal analysis was utilised to measure the composition dependence of liquidus, solidus and γ′ solvus temperatures. Over the range of composition characteristic of the most advanced commercial single crystal alloys, synergistic interactions existing between select constituent elements were found to mitigate the severity of Re and W segregation during dendritic solidification. Minor additions of carbon, in the range of 0·05–0·15 wt-%, were also found to reduce the degree of Re and W segregation during solidification. In both instances, controlling the extent of Re and W segregation during solidification was shown to strongly influence the tendency of the alloy to form macroscopic grain defects, such as freckles, during unidirectional solidification. Moreover, precipitation of primary carbides within the mushy zone during solidification was also found to impact the solidification characteristics of the alloy. The implications of these alloying approaches for developing novel, high refractory content, single crystal superalloys compositions that are amenable for manufacturing are discussed.
