Effective solution treatment can result in improved creep performance of superalloys

Herein, we demonstrate the creep performance of a turbine disk superalloy - FGH100L - at 705 °C and 897 MPa. The effect of solution treatment and cooling rate on the microstructure, fracture and creep performance is presented in detail. The microstructure and fracture are characterized by optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results reveal that instead of air cooling (AC), after solution treatment (ST), the combination of slow and fast cooling improves the creep performance of the alloy at 705 °C and 897 MPa. Both during AC and the combination of slow and fast cooling, followed by ST, the creep process is dominated by the accumulation of dislocations and stacking faults, cutting through the γ′ phase. The microstructural evolution is the main cause of creep acceleration, which mainly manifests as coarsening and morphology change of the γ′ phase. Our proposed heat treatment scheme generates the serrated grain boundaries, which play a vital role in improving the creep performance. In the case of AC, the creep pores sprout and develop into wedge-shaped cracks at the trigeminal intersection of the grain boundary, while the combination of slow and fast cooling results in opening-mode cracks at the grain boundary and carbide interface. Both creep ruptures, under two different heat treatment processes, are intergranular fractures.