Abstract:

Two alloys with different Ta and Al contents were applied to study the influence of Ta/Al ratio on the microstructural evolution and creep deformation under high temperature. The increase of Ta/Al ratio made the γ/γ′ lattice misfit more negative and enhanced the volume fraction of γ′ phase, which produced cubic and small γ′ phase in the initial microstructures. These initial tiny γ′ phases impeded the dislocations movement and delayed the course of complete rafted γ′ phase during the origination of creep deformation, which prolonged the time of the primary creep stage. Moreover, the increase of Ta/Al ratio and addition of Ru produced the denser and stable dislocation networks, the high APB energy and better solution strengthening, which hindered the climbing and sliding of dislocations, and restrained the formation of superdislocations in the γ′ precipitate. The second creep stage was extended, and the minimum creep rate was reduced. Hence, the increase of whole creep life of the alloy containing high Ta/Al ratio was attributed to the prolongation of the primary and second creep stages, and the low minimum creep rate. The appearance of the topological inversion phenomenon during the tertiary creep stage was the primary cause for the sudden increase of the creep strain rate of the alloy containing low Ta/Al ratio. However, the high creep strain rate of the alloy containing high Ta/Al ratio during the tertiary creep stage was related to the occurrence and extending of the cracks near the voids. Both alloys would lose efficacy within 20 h-30 h.

Key words: Ni-based superalloys, Ta/Al ratio, High temperature creep, Interfacial dislocation networks, γ′ rafting