Effect of the γ′ volume fraction on the creep strength of Ni-base superalloys

Abstract Three single-crystalline Ni-base superalloys with varying content of the γ′ phase are investigated with respect to their microstructure and creep behaviour at 1000°C. It is shown by convergent beam electron diffraction, X-ray diffraction and energy-dispersive X-ray spectroscopy that the composition of the matrix and precipitates as well as the lattice misfit between both phases are similar for all three model alloys despite a variation of the γ′ content from about 50 to about 65%. This allows to study the influence of the precipitate volume fraction on high-temperature behaviour in separation from other microstructural parameters. Highest creep strength is found for the alloy with intermediate particle content (about 58%), which is significantly below the particle volume fraction of contemporary single-crystal superalloys such as CMSX-4.