Primary microstructure, microsegregation and precipitates characterization of an as-cast new type γ-γ′ Co-Al-Mo-Nb cobalt-based superalloy

Present paper concerns primary structure of new type of tungsten-free cobalt-based superalloys with formula Co-Al-Mo-Nb. Due to replacement of W by addition of Mo and Nb, the desirable dual phase structure of γ/γʹ should be formed after heat treatment of this alloy. In analyzed case, the alloy in as cast state was described. The Co-10Al-5Mo-2Nb (at%) alloy was casted via induction melting process. The specimens were cut from “foot“ area of the rod and analyzed from phases and chemical point of view by XRD and EDS analysis. Detailed analysis of primary microstructure by light and scanning microscopy observations were performed. Obtained data revealed that in as cast state, the main phases detected in the alloy were solid solution of Co(Al,Mo,Nb) and Mo with Nb reach precipitations, probably with formula of Co3(Mo,Nb). The morphology of observed interdendritic precipitations is typical for eutectic reaction.