Effect of Ta and Ni on γ′ phase morphology and compression behavior of Co-8.8Al-9.8W superalloys

To investigate the effect of the γ′ phase morphology of cobalt-based superalloys on the plastic deformation behavior of the superalloys, Co-8.8Al-9.8W-2X (X=Ta, Ni) alloys were prepared to obtain superalloys with different morphologies of γ′ phases. The microstructure and room temperature compression behavior of superalloys were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the γ′ phase particles of 2Ta alloy are cubic, while that of 2Ni alloy is spherical. The compressive strength of 2Ta and 2Ni alloys are almost the same, but the hardness of 2Ta alloy is higher than that of 2Ni alloy, while the plastic deformability is significantly worse. 2Ta alloy exhibits quasi-cleavage fracture during compression, while 2Ni alloy showed a cleavage fracture, and amount of slip bands were found easily on the fracture surface of 2Ni alloy. The deformations of 2Ni alloy and 2Ta alloy were dominated by dislocations shearing γ′ phase particles. The γ′ phase of the 2Ni alloy underwent rafting, while that of 2Ta alloy did not change significantly.