Influence of withdrawal rate on the microstructure of Ni-base single-crystal superalloys containing Re and Ru

The influence of elevated withdrawal rate on the microstructure and segregation behavior of Ni-base single-crystal superalloys containing Re and Ru is investigated. The experimental superalloys are processed under a high thermal gradient of approximately 250 K/cm and withdrawal rates between 10 and 500 μm/s. With increasing withdrawal rate, the dendritic structures and γ′ precipitates in as-cast microstructures are apparently refined. Electron-probe microanalyzer (EPMA) results indicate that the degree of segregation for the constituent elements (e.g. Al, Ta, W, Re etc.) increases initially and then decreases with increasing withdrawal rate. In addition, the Re and Ru additions obviously increase the amounts of γ–γ′ eutectic and the tendency of segregation for Al and Ta.

► We characterize the as-cast microstructure of Re- and Ru-containing single-crystal superalloys.
► Dendrite structure is greatly refined with increasing withdrawal rate.
► The segregation of alloying element increases firstly, and then decreases with increasing withdrawal rates.
► Re and Ru additions promote the tendency of dendritic segregation, and increase the volume fraction of eutectic.