Abstract:At temperatures ranging from 760 to 1100 °C, the tensile properties of a nickel-based third generation single crystal superalloy DD9 with [100], [120] and [110] orientations were studied. The microstructures and fracture surfaces were observed by OM, SEM and TEM. Results show that the tensile strength of [100] specimen is higher than that of [120] and [110] specimens at 760 and 850 °C; while at the temperatures higher than 980 °C, the tensile strength of all specimens has little difference. The fracture mechanisms of [100], [120] and [110] specimens are the same at 760 and 980 °C. At 1100 °C, the fracture surfaces of [100] and [120] specimens are characterized by dimple features; while [110] specimen shows mixed quasi-cleavage and dimple featured fracture surfaces. At 760 °C, obvious superlattice stacking faults (SSFs) are observed only in [100] specimen; while at 1100 °C, the dislocation configurations of all specimens are similar. The difference in the number of potential active slip systems in [100], [120] and [110] specimens during the tensile deformation process is the main reason for the transverse tensile anisotropy.

Key words: third generation single crystal superalloy; DD9; transverse tensile properties; anisotropy; fracture surface