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The effect of solution treatment on the microstructure and creep properties of forged TiAl–Nb alloys was investigated. The results showed that the microstructure of forged alloy mainly consisted of γ/α2 lamellar colonies and fine equiaxed recrystallized γ/α2 grains. During the solution treatment the microstructure of the alloy transformed into a fully lamellar structure due to the lamellar colonies growth by consuming equiaxed grains. Compared with the forged alloy the creep life of the solution treated alloy at 800 ​°C/220 ​MPa increased from 116 ​h to 339 ​h. The better creep resistance may be attributed to the transform of fine equiaxed γ/α2 grain to the lamellar colonies with serrated grain boundaries due to the solution treatment. The deformation mechanism of the solution treated alloy during creep is considered to be dislocation slipping within the lamellar γ/α2 phases, and the dislocation movement may be hindered by the γ/α2 interface and the formation of dislocation tangles. The interaction of the dislocations with the tangles may increase the resistance of the dislocation motion and hence improve the creep resistance of the alloy. It was found that during the creep of the forged alloys the cracks mainly initiated at the equiaxed grain, and in the solution treated alloy the cracks initiated at the grain boundaries. As creep continued the cracks propagated and connected to each other, leading to the damage and rupture of the forged and solution treated alloys.

In order to understand the influence of Ru and Re on the concentration distributions of elements in γ′ and γ phases, the partitioning behaviors of elements in various alloy are investigated by means of atom probe tomography (APT). Results show that the elements Al, Ta and Ni are enriched in γ′ phase, while the elements Co, Cr, Mo, W, Re and Ru are enriched in γ matrix phase. Adding Ru may decrease the partitioning ratio of elements in γ and γ′ phases. Wherein, when Ru atoms dissolve into γ′ phase to substitute the Al atoms, some Re, Mo and W atoms adhered in the round of Ru atoms, under the hybridization effect of d orbit, may dissolve into γ′ phase, which is thought to be the main reason of Ru decreasing the partitioning ratios of γ′ and γ phases. When adding Re into the alloy, the Re atoms with low diffusion coefficient may hinder the diffusion of other atoms away from γ′ phase during the growth of γ′ phase, which is thought to be the main reason of decreasing the partitioning ratios of elements in γ and γ′ phase. Keywords: Nickel-base single crystal superalloy, Ruthenium, Rhenium, Atom probe