Design and characterization of Co-Ti-based superalloys with V, Cr, and Mo

Abstract

Co-Al-W-based superalloys show some strengths such as higher melting points of Co than that of Ni, positive lattice misfit between γ/γ' microstructure, high-temperature strength, and superior creep property. But the narrow composition range of Co-Al-W and a large amount of W restrict its application. The Co-Ti is an only known binary system forming thermodynamically stable γ/γ' microstructure. Thus, Co-Ti-based superalloys are promising alternatives to Co-Al-W-based superalloys. Low γ' phase dissolution temperature around 1300K, γ' coarsening, and low γ' volume fraction at 1170K of Co-Ti binary system is a problem to be solved. Therefore, in this thesis, microstructural characterization and mechanical and thermal properties testing were performed by adding V, Cr, and Mo to the Co-Ti binary system to design a Co-Ti-based superalloys that overcome the drawbacks. Characterization techniques such as corelative electron Microscopies especially Atom Probe Tomography which has near-atomic resolution and ppm level of chemical sensitivity with 3D modeling in the nano-scale were conducted.