Effect of Si on the Solidification Segregation Behavior of a New Ni-Co-Based Superalloy

Herein, the effects of Si addition on the microstructure and solidification behavior of a new Ni-Co-based superalloy are investigated. The microstructure of the as-cast alloys is mainly composed of gamma, gamma ', (gamma-gamma ') eutectics, and MC-type carbides. The results demonstrate that Si addition significantly decreases the size and volume fraction of (gamma-gamma ') eutectics, while promoting the formation of Si-rich phase precipitated in front of the (gamma-gamma ') eutectics. The formation of a Si-rich phase is induced by the rejection of Ti and Si into the residual liquid during the gamma matrix formation. With the increase in Si content, the size distribution of (gamma-gamma ') eutectics decreases due to the formation of the Si-rich phase consuming the forming element of (gamma-gamma ') eutectics. The solidus and liquidus temperatures of the alloy decrease with the increase in Si. However, the range of melting temperature increases. The Si addition promotes the segregation of alloying elements, and Si tends to segregate in the interdendritic region.