Creep deformation-induced antiphase boundaries in L12-containing single-crystal cobalt-base superalloys

Creep-induced antiphase boundaries (APBs) in new Co-base single-crystal superalloys with coherent embedded L12-γ′ precipitates have been observed. APBs formed during single-crystal tensile creep tests performed at 900 °C under vacuum at stresses between 275 and 310 MPa. The alloys investigated contained 30-39 at.% Ni, which was added to the Co-Al-W ternary system to expand the γ-γ′ phase field and increase the γ′-solvus. Transmission electron microscopy (TEM) using two-beam conditions with fundamental and superlattice reflections was performed for defect characterization. The Burgers vector b of dislocations associated with the APBs was determined to be of type b = a0/2[011] and a0/2[011¯]. The displacement vectors, R, of the APBs matched the dislocation Burgers vectors, with R = b = a0/2[011]. APBs were observed in nearly every precipitate beyond 0.5% creep strain for the compositions investigated. The implications for high-temperature properties are discussed.