Effect of γ′ size on the high-temperature low-stress creep of nickel-based single-crystal superalloys

Abstract

Nickel-based single crystal superalloys exhibit excellent high temperature mechanical properties due to their unique γ′-γ dual phase microstructure. Microstructure design is the major strategy for increasing their properties. However, the design strategy for the size of the γ′ phase is still lacking. This work investigates the effect of γ′ cuboid size on the creep-rupture life of nickel-based single crystal superalloys via a comparative experiment of two alloys of similar γ′ phase volume fractions and different elemental compositions. The alloy with smaller γ′ phase cuboids exhibits a creep-rupture life twice as long as the alloy with an average cuboid size 30 % larger. In addition, a smaller average γ′ phase cuboid size also contributes to a lower density of the dislocations, a smaller spacing of the raft and lower content of the topologically closed packed phases. The reasons behind these different mechanical properties and microstructures are discussed.