Design of gamma-prime-strengthened Co-based Superalloys: Where we are and where we need to go

Since the first report of a stable two-phase g-g’ (FCC-L12) phase field in ternary Co-Al-W in 2006, there has been significant research effort in developing this new class of Co-based g’-strengthened superalloys for high temperature applications. Much of the focus has been on characterizing and improving high temperature properties such as the g’ solvus temperature, high temperature strength and creep resistance, corrosion and oxidation behavior. Much of this work has been conducted experimentally utilizing the wealth of knowledge of Ni-based superalloys gathered over the last several decades. Efforts into developing effective modeling tools, such as thermodynamic and diffusion databases, have been less abundant; however there have been some valuable contributions to understanding the fundamentals of these new alloys, realized via ab initio calculations and key experimental phase equilibria investigation, and thermodynamic assessments. This work will look at the currently available modeling tools, specifically Calphad-type composition and temperature dependent descriptions of thermodynamic and other thermophysical properties, to explore their effectiveness in developing new alloys. Available thermodynamic databases are investigated for accuracy of predictive phase equilibria calculations, specifically in identifying alloy compositions with increased g’ solvus temperatures. Efforts to develop descriptions for other essential properties, such as diffusivity, molar volume, and elastic moduli are also discussed. The shortcomings of these databases are discussed; and specific areas are identified where additional experimental and computational investigation could make a significant impact on the effectiveness of the next generation of computational modeling tools for this promising new alloy system