The creep behavior of a disk superalloy under different stress conditions

Throughout this project, a candidate nickel-based turbine disk superalloy was prepared by spray forming process. After creep testing, samples were carried out at 705 °C/750 MPa, 705 °C/793 MPa and 705 °C/897 MPa. The microstructure and creep properties of the alloy were investigated using transmission electron microscope (TEM). The results show that the creep rate of the alloy was improved and the creep life decreased significantly when the stress increased from 750 MPa to 793 MPa and 897 MPa. According to the result, the alloy has high stress index. Furthermore, when the stress was as relatively low as 750 MPa or 793 MPa, the creep mechanism of the alloy was dislocation shearing into γ′ phases; when the stress was as high as 897 MPa, the creep mechanism was stacking faults and micro-twins cutting γ′ phases. Under different stress conditions, the tertiary creep has a significant impact on the total deformation quantity and creep life of the alloy and the rafting of γ′ phase is the main reason of the creep acceleration. With the increasing applied stress, rafting of γ′ phase becomes obvious and it accelerates the tertiary creep deformation but reduces the creep properties of the alloy.