Creep behavior and deformation mechanisms of a fourth-generation Ni-based single crystal superalloy at intermediate temperatures

Abstract

The creep behavior and microscopic deformation mechanisms of a fourth-generation Ru-containing Ni-based single crystal superalloy were investigated at intermediate temperature of 850 °C under high applied stresses of 620, 700, and 750 MPa. SEM and TEM analyses showed that the alloy exhibited a mixed fracture mode mainly composed of micropore coalescence and shear. The γ′ precipitates exhibited stress-dependent rafting, forming relatively regular rafts at lower stress and elongated structures parallel to the loading direction at higher stresses. The alloy shown a low stacking fault energy (SFE) in the γ matrix, as evidenced by a high density of extended stacking faults (SFs) and dislocation configurations in both the γ channels and the γ′ phase. With increasing stress, a/3<112> leading Shockley partial dislocations were activated to shear the γ′ phase and generate SFs. The resulting SF locks and dislocation pile-ups impeded subsequent dislocation motion and provided additional resistance to creep. These low-SFE–controlled dislocation mechanisms govern the creep deformation of this fourth-generation alloy in the intermediate temperature high stress regime and provide mechanistic guidance for the design of high performance single crystal superalloys in service conditions.