Intermediate temperature creep damage mechanisms of a directionally solidified Ni-based superalloy

Microstructure evolution and damage mechanisms during the creep deformation of a directionally solidified Ni-based superalloy were evaluated. The creep deformation behaviour was studied along the longitudinal direction (i.e. along the solidification direction), at a moderate temperature of 870 degrees C, and applied stresses ranging from 310 to 450 MPa concerning the service conditions in industrial gas turbine blades. It was shown that at the lower stress levels of about 310 MPa, the average creep strain rate decreased by two orders of magnitude, while tertiary creep appeared as the dominant stage. Progressive coarsening of gamma' precipitates was also observed, meantime gamma' precipitate shearing was confirmed to occur over the evaluated range of stresses.