Effect of Ru on microstructure evolution of the fourth generation nickel-based single crystal superalloy DD22 during long-term aging

Abstract

The morphological evolution of γ′ phase, the precipitation of TCP phases and the evolution of the interfacial dislocation networks in DD22 nickel-based single crystal superalloys with different Ru contents (3% and 5%, mass fraction) were investigated by transmission electron microscopy and field emission scanning electron microscopy during long-term aging at 1130 ℃. The results show that γ′ phase of 5Ru alloy are smaller in size and more regular in shape than that of 3Ru alloy. The mismatch of γ/γ′ phases is larger in 5Ru alloy, and the high content of Ru causes the reverse distribution of elements such as Re and Mo. During long-term aging at 1130 ℃, the coarsening rate, dissolution rate and rafting rate of γ′ phase in 5Ru alloy are lower than those of 3Ru alloy. There is still no TCP phase precipitation in 5Ru alloy after long-term aging for 1000 h, while a small amount of TCP phase is precipitated in 3Ru alloy after long-term aging for 50 h. With the prolongation of long-term aging time, the number and size of TCP phases both increase. Compared with 3Ru alloy, the interfacial dislocation networks of 5Ru alloy are denser and more regular after long-term aging for 1000 h. Above all, the reverse distribution of elements and low diffusion coefficient of Ru make 5Ru alloy exhibit higher microstructural stability than 3Ru alloy.

Keywords

• dd22 nickel-based single crystal superalloy
• ru content
• long-term aging
• dislocation networks
• microstructural stability