Creep damage characterization of Ni-based superalloy by acoustic nonlinearity

The creep damage of Ni-based superalloy has been experimentally investigated by acoustic nonlinearity measured by the finite amplitude method. The creep test is conducted and interrupted after a specified fraction of creep life time. The cuboidal γ′ precipitates coarsen preferentially in the direction perpendicular to the applied stress axis. The aspect ratio (a/b) of the γ′ precipitate increases monotonously with creep duration. The increase in acoustic nonlinearity is discussed in relation to the directional coarsening of the γ′ precipitates, which proves to be closely related to the scattering and distortion of the ultrasonic waves. We have determined that acoustic nonlinearity is a potential diagnostic method for determining creep damage in Ni-based superalloys.