Solid-State Joining of Dissimilar Single Crystal and Polycrystalline Ni-Based Superalloys Using Field-Assisted Sintering Technology

Field assisted sintering technology (FAST) was studied as a method to solid-state join a single crystal Ni-based superalloy (PW1429) to the same single crystal superalloy (PWA1429), a different single crystal superalloy (PWA1480), and a polycrystalline superalloy (CM247LC), without localized melting unlike friction welding. Such a joining method is desired to repair cracked gas turbine blades. The joined interphase was void-free; the γ^′ precipitation morphology varied along the interphase thickness, to bridge between the different chemical compositions of the two parts. Room temperature tensile testing indicated that bonding strengths are comparable with those of the parent materials. Fracture occurred at the interface when two single crystal components are joined, while fracture occurred away from the interface when a single crystal PWA1429 and a polycrystalline part are joined. The FAST-joined parts were also tensile tested at 700 ^∘C, after a double-aging heat treatment to recover the desired cuboidal γ^′ precipitate shape. The joined PWA1429-CM247LC samples and PWA1429-PWA1429 samples showed moderate strength degradation at high temperature from the values measured at room temperature, while the joined PWA1429-PWA1480 samples exhibited large degradation. These results indicate the influence of crystalline mismatch. Further interphase improvement can be pursued through a post annealing process.