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

Nickel-based single crystal superalloys exhibit excellent high temperature mechanical properties due to their unique gamma '-gamma dual phase microstructure. Microstructure design is the major strategy for increasing their properties. However, the design strategy for the size of the gamma ' phase is still lacking. This work investigates the effect of gamma ' cuboid size on the creep-rupture life of nickel-based single crystal superalloys via a comparative experiment of two alloys of similar gamma ' phase volume fractions and different elemental compositions. The alloy with smaller gamma ' 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 gamma ' 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.