Stress rupture behavior of service-exposed and rejuvenated DZ417G blades under two representative conditions

The stress rupture life of blade samples repaired by process I is about three times that of the service-exposed samples, both under 760℃/725 MPa and under 980℃/216 MPa. Three primary dislocation configurations were identified within the γ’ phases. Compared with the service-exposed sample tested under 980℃/216 MPa, the reduction of dislocation configurations in γ’ phases was observed in the repaired sample. This phenomenon is ascribed to the discrepancy of γ′ configurations in above samples. Wavy boundary of the rafted γ′ in the repaired sample can effectively block dislocations from shearing into the γ′ phases. In addition, four types of transverse cracks were observed in sample tested under 980°C/216 MPa: cracks initiating in the eutectic phase and eutectic/γ boundary, MC carbides, rafted γ’ phases, as well as oxidation-induced cracking. Rejuvenation process I, which reduces eutectic phases and controls the γ′ configuration in blade, can effectively prolong the stress rupture life of blade at 980°C/216 MPa. Crack initiation at MC carbides is the primary failure mechanism for samples tested under 760℃/725 MPa. The γ’ configuration controlled by process I enhances the deformation resistance of sample at 760°C/725 MPa. This slows down the rate of dislocation accumulation in brittle MC carbides, which retards the fracture of the repaired samples.