Effects of Different Heat Treatments on the Microstructures and Creep Properties of GH4169 Superalloy

Experiments were conducted to evaluate the effects of different heat treatments on the microstructures and creep properties of GH4169 alloy. In order to study the strengthening effect of the delta phase, three different heat treatments were performed in this research. (1) High standard treatment (namely, HST), i.e., 960 A degrees C x 2 h/air cooling (AC) + 720 A degrees C x 8 h/furnace cooling (FC) at 55 A degrees C/h to 620 A degrees C + 620 A degrees C x 8 h/AC. (2) Standard treatment (namely, ST), i.e., 960 A degrees C x 1 h/AC + 720 A degrees C x 8 h/FC at 55 A degrees C/h to 620 A degrees C + 620 A degrees C x 8 h/AC. (3) Direct aging treatment (namely, DA), i.e., 720 A degrees C x 8 h/FC at 55 A degrees C/h to 620 A degrees C + 620 A degrees C x 8 h/AC. In HST specimen, it is observed that the delta phases exist not only at the boundaries but also locate inside the grains. However, few delta phases can be observed in DA specimen. All the samples were creep tested to failure under the condition of 650 A degrees C/725 MPa. The DA alloy exhibited the best creep property and the creep rupture life was as long as 169 h. The creep rupture life of the ST alloy was the shortest, which is only about 88 h. The reasons can be summarized as the amount of the strengthening phases, the compactness of the boundaries, the fixing effect of the delta phase and the favorable strength coordination. All the points are closely related with the delta phase. It is reasonable to conclude that the quantity and distribution of delta phase have great influence on the creep properties of GH4169 alloy. Moreover, the fracture modes of the three samples are also discussed in this paper.