The morphologies of directionally solidified nickel-based superalloy after heat treatment and damage mechanism of the alloy at 760 ℃ and 700 MPa for different creep duration were investigated by creep property test and microstructure observation. The results reveal that after heat treatment

the sizes of γ′ phases between interdendritic region and dendrite arms are greatly different

where the coarse and fine γ′ phase exist in interdendritic and dendrite arm region

respectively. The cubic γ′ phase does not form raft structure after the alloy creep rupture at 760 ℃ and 700 MPa

and the closer to the fracture area

the more severe γ′phase distortion

which is attributed to the necking to a greater extent at the fracture during the creep. In the later stage

cracks in the alloy are firstly initiated and propagated at grain boundary and eutectic structure that is not eliminated

where the grain boundary at a 45 angle to the stress axis suffers the higher shear stress

enhancing creep damage probability.