Role of size and amount of γ' phase on creep properties of Waspaloy

The creep tests of Waspaloy were carried out at 650 °C under 780 MPa with different sizes and amounts of primary γ' phase. The creep samples were preheated at various temperatures for different times, and the microstructures with the same amount and different size of the primary γ' phase were obtained, as well as the same size and different amount. The creep behavior of the Waspaloy was analyzed. It was found that the creep life and the interval of steady-state creep stage of the Waspaloy decreases dramatically with the increase of the amount, and decreases slowly with the increase of the size of the primary γ' phase. Investigations of the creep fracture indicate that the fracture mode is the mixed intergranular and transgranular fracture. The results of electron backscattered diffraction (EBSD) near the fractures show that geometrically necessary dislocation (GND) density increases with the increase of size and amount of primary γ' phase. In addition, the higher GND density tends to appear at the grain boundaries and twin boundaries, which leads to the crack nucleation and propagation along the grain boundaries and twin boundaries. Transmission electron microscopy (TEM) analysis shows that the Orowan looping coupled with the stacking faults and microtwins shearing the γ' phase are the main deformation mechanism.