An Overview on Co-Base Alloys for High Temperature Applications

Abstract

The article outlines the evolution, over the last half a century, of Co-base superalloys. Recent developments have led to the emergence of these alloys as a promising alternative to high temperature commercial Ni-base superalloys that are used in fabricating components of gas turbine engines that power passenger/military aircrafts, ships and power plants. The materials used in these engines experience temperatures as high as 1600°C combined with high stresses and corrosive environment often under high pressure. Earlier generations of Co-base alloys have niche applications where resistance to corrosion/oxidation rather than strength is needed as these were primarily strengthened through solid solution and dispersion of carbides and borides. Discovery of γ/γ′ microstructure in Co-base alloys akin to that present in Ni-base superalloys has opened opportunities for developing new classes of high temperature, high strength superalloys. In this review, we first briefly summarize the status of solid solution strengthened Co-base superalloys followed by a review of rapidly evolving Co-based superalloys that are strengthened by the γ′ precipitation in a γ matrix.